Ultra-faint dwarf galaxies (UFDs) are the faintest known galaxies and due to their incredibly low surface brightness, it is difficult to find them beyond the Local Group. We report a serendipitous discovery of an UFD, Fornax UFD1, in the outskirts of NGC 1316, a giant galaxy in the Fornax cluster. The new galaxy is located at a projected radius of 55 kpc in the south-east of NGC 1316. This UFD is found as a small group of resolved stars in the Hubble Space Telescope images of a halo field of NGC 1316, obtained as part of the Carnegie-Chicago Hubble Program. Resolved stars in this galaxy are consistent with being mostly metal-poor red giant branch (RGB) stars. Applying the tip of the RGB method to the mean magnitude of the two brightest RGB stars, we estimate the distance to this galaxy, 19.0 +- 1.3 Mpc. Fornax UFD1 is probably a member of the Fornax cluster. The color-magnitude diagram of these stars is matched by a 12 Gyr isochrone with low metallicity ([Fe/H] ~ -2.4). Total magnitude and effective radius of Fornax UFD1 are Mv ~ -7.6 +- 0.2 mag and r_eff = 146 +- 9 pc, which are similar to those of Virgo UFD1 that was discovered recently in the intracluster field of Virgo by Jang & Lee (2014).Fornax UFD1 is the most distant known UFD that is confirmed by resolved stars. This indicates that UFDs are ubiquitous and that more UFDs remain to be discovered in the Fornax cluster.
This is the second paper of a series aimed to study the stellar kinematics and population properties of bulges in highly-inclined barred galaxies. In this work, we carry out a detailed analysis of the stellar age, metallicity and [Mg/Fe] of 28 highly-inclined ($i > 65^{o}$) disc galaxies, from S0 to S(B)c, observed with the SAURON integral-field spectrograph. The sample is divided into two clean samples of barred and unbarred galaxies, on the basis of the correlation between the stellar velocity and h$_3$ profiles, as well as the level of cylindrical rotation within the bulge region. We find that while the mean stellar age, metallicity and [Mg/Fe] in the bulges of barred and unbarred galaxies are not statistically distinct, the [Mg/Fe] gradients along the minor axis (away from the disc) of barred galaxies are significantly different than those without bars. For barred galaxies, stars that are vertically further away from the midplane are in general more [Mg/Fe]--enhanced and thus the vertical gradients in [Mg/Fe] for barred galaxies are mostly positive, while for unbarred bulges the [Mg/Fe] profiles are typically negative or flat. This result, together with the old populations observed in the barred sample, indicates that bars are long-lasting structures, and therefore are not easily destroyed. The marked [Mg/Fe] differences with the bulges of unbarred galaxies indicate that different formation/evolution scenarios are required to explain their build-up, and emphasizes the role of bars in redistributing stellar material in the bulge dominated regions.
We examine the HI-to-stellar mass ratio (HI fraction) for galaxies near filament backbones within the nearby Universe ($d <$ 181 Mpc). This work uses the 6 degree Field Galaxy Survey and the Discrete Persistent Structures Extractor to define the filamentary structure of the local cosmic web. HI spectral stacking of HI Parkes all sky survey observations yields the HI fraction for filament galaxies and a field control sample. The HI fraction is measured for different stellar masses and fifth nearest neighbour projected densities ($\Sigma_{5}$) to disentangle what influences cold gas in galaxies. For galaxies with stellar masses log($M_{\star}$) $<$ 11 M$_{\odot}$ in projected densities 0 $\leq$ $\Sigma_{5}$ $<$ 3 galaxies Mpc$^{-2}$, all HI fractions of galaxies near filaments are statistically indistinguishable from the control sample. Galaxies with stellar masses log($M_{\star}$) $\geq$ 11 M$_{\odot}$ have a systematically higher HI fraction near filaments than the control sample. The greatest difference is 0.75 dex, which is 5.5$\sigma$ difference at mean projected densities of 1.45 galaxies Mpc$^{-2}$. We suggest that this is evidence for massive galaxies accreting cold gas from the intrafilament medium that can replenish some HI gas. This supports cold mode accretion where filament galaxies with a large gravitational potential can draw gas from the large-scale structure.
We present new ALMA observations of the [OIII]88$\mu$m line and high angular resolution observations of the [CII]158$\mu$m line in a normal star forming galaxy at z$=$7.1. Previous [CII] observations of this galaxy had detected [CII] emission consistent with the Ly$\alpha$ redshift but spatially slightly offset relative to the optical (UV-rest frame) emission. The new [CII] observations reveal that the [CII] emission is partly clumpy and partly diffuse on scales larger than about 1kpc. [OIII] emission is also detected at high significance, offset relative to the optical counterpart in the same direction as the [CII] clumps, but mostly not overlapping with the bulk of the [CII] emission. The offset between different emission components (optical/UV and different far-IR tracers) is similar to what observed in much more powerful starbursts at high redshift. We show that the [OIII] emitting clump cannot be explained in terms of diffuse gas excited by the UV radiation emitted by the optical galaxy, but it requires excitation by in-situ (slightly dust obscured) star formation, at a rate of about 7 M$_{\odot}$/yr. Within 20 kpc from the optical galaxy the ALMA data reveal two additional [OIII] emitting systems, which must be star forming companions. We discuss that the complex properties revealed by ALMA in the z$\sim$7.1 galaxy are consistent with expectations by recent models and cosmological simulations, in which differential dust extinction, differential excitation and different metal enrichment levels, associated with different subsystems assembling a galaxy, are responsible for the different appearance of the system when observed with different tracers.
We quantify the number density of compact massive (M > 5x10^10 M_sun) galaxies at intermediate redshifts (0.2<z<0.6) in the equatorial SDSS Stripe 82 region (~250 sq. degrees). This is the largest volume probed up to date allowing to decrease the effect of cosmic variance. Structural parameters are obtained in the i-band using the CFHT Stripe 82 (CS82) survey with an exquisite median seeing of ~0.6". We explore a variety of definitions of compactness present in the literature. We find that the absolute number of compact galaxies is very dependent on the adopted definition, and can change up to a factor of >10. However, we systematically measure a factor of ~5 more compacts at the same redshift than what was previously reported on smaller fields with HST imaging, more affected by cosmic variance. This means that the decrease in number density from z~1.5 to z~0.2 might be only of a factor of ~2-5, significantly smaller than what previously reported: this supports progenitor bias as the main contributor to the size evolution. This decrease is roughly compatible with the predictions from recent numerical simulations. Only extreme compact galaxies (Reff < 1.5x(M/10^11 M_sun)^0.75 and M > 10^10.7 M_sun) seem to drop in number by a factor of ~20 and therefore probably experience a noticeable size evolution.
Under a MONDian view, astrophysical systems are expected to follow Newtonian dynamics whenever the local acceleration is above the critical $a_{0}=1.2 \times 10^{-10} m s^{-2}$, and enter a modified regime for accelerations below this critical value. Indeed, the dark matter phenomenology appears always, and only, at low accelerations. It is standard to find the $a<a_{0}$ regime towards the low density outskirts of astronomical systems, where under a Newtonian interpretation, dark matter becomes conspicuous. Thus, it is standard to find, and to think, of the dense central regions of observed systems as purely Newtonian. However, under spherical symmetry in the MONDian as in the Newtonian case, the local acceleration will tend to zero as one approaches the very centre of a mass distribution. It is clear that for spherically symmetric systems, an inner $a<a_{0}$ region will necessarily appear interior to a critical radius which will depend on the details of the density profile in question. Here we calculate analytically such a critical radius for a constant density core, and numerically for a cored isothermal profile. Under a Newtonian interpretation, such a central MONDian region will be interpreted as extra mass, analogous to the controversial black holes sometimes inferred to lie at the centres of globular clusters, despite an absence of nuclear activity detected to date. We calculate this effect and give predictions for the "central black hole" mass to be expected under Newtonian interpretations of low density Galactic globular clusters.
The Galactic Central Molecular Zone (CMZ) is a region containing massive and dense molecular clouds, with dynamics driven by a variety of energy sources including a massive black hole. It is thus the nearest template for understanding physical processes in extragalactic nuclei. The CMZ's neutral interstellar gas has been mapped spectrally in many neutral atomic and molecular gas tracers, but the ionized and CO-dark H2 regions are less well traced spectroscopically. We mapped the fine structure line of C+ at 158 microns, [C II], to identify and characterize features of the ionized gas in the CMZ, including UV irradiated neutral gas, photon dominated regions (PDRs), CO-dark H2 gas, and highly ionized gas. We observed the [C II] 158-micron fine structure line with high spectral resolution using Herschel HIFI with two perpendicular On-the-Fly strip scans, along l = -0.8 to +0.8 and b = -0.8 to +0.8, both centered on (l,b) = (0,0). We analyzed the spatial-velocity distribution of the [C II] data and compared them to those of [C I] and CO, and to dust continuum maps, in order to determine the properties and distribution of the UV irradiated gas and its dynamics within the CMZ. The longitude- and latitude-velocity maps of [C II] trace portions of the orbiting open gas streams of dense molecular clouds, the cloud G0.253+0.016, also known as the Brick, the Arched Filaments, and the ionized gas near Sgr A and Sgr B2. We use the [C II] and auxiliary data to determine the physical and dynamical properties of these CMZ features. The [C II] emission arises primarily from dense PDRs and highly ionized gas, and is an important tracer of the kinematics and physical conditions of this gas.
We explore constraints on the statistical relationship between the radial size of galaxies and the radius of their host dark matter halos from $z\sim 0.1-3$ using the GAMA and CANDELS surveys. We map dark matter halo mass to galaxy stellar mass using empirical relationships from abundance matching, applied to the Bolshoi-Planck dissipationless N-body simulation. We define SRHR$\equiv r_e/R_h$ as the ratio of galaxy radius to halo virial radius, and SRHR$\lambda \equiv r_e/(\lambda R_h)$ as the ratio of galaxy radius to halo spin parameter times halo radius. At $z\sim 0.1$, we find an average value of SRHR$\lambda \simeq 0.45$ with very little dependence on stellar mass. We find that the average values of SRHR$\lambda$ derived from all five fields of CANDELS at $z\sim 0.4-3$ are a factor of two or more higher than those derived from local surveys. Within the CANDELS survey, SRHR and SRHR$\lambda$ show a mild decrease over cosmic time. We find that the dispersion in $(\lambda R_h)$ is remarkably consistent with the distributions of observed sizes in stellar mass bins over $z\sim 0.1-3$, for both the GAMA and CANDELS samples. This places limits on the galaxy-to-galaxy scatter in SRHR$\lambda$. We find hints that at high redshift ($z\sim 2-3$), SRHR$\lambda$ is lower for more massive galaxies, while it shows no significant dependence on stellar mass at $z\lesssim 0.5$. We discuss the physical interpretation and implications of these results.
We present a photometric study of PGC 1000714, a galaxy resembling Hoag's Object with a complete detached outer ring, that has not yet been described in the literature. Since the Hoag-type galaxies are extremely rare and peculiar systems, it is necessary to increase the sample of known objects by performing the detailed studies on the possible candidates to derive conclusions about their nature, evolution, and systematic properties. We therefore performed surface photometry of the central body by using the archival near-UV, infrared data and the new optical data (BVRI). This current work has revealed for the first time an elliptical galaxy with two fairly round rings. The central body follows well a r^(1/4) light profile, with no sign of a bar or stellar disc. By reconstructing the observed spectral energy distribution, we recover the stellar population properties of the central body and the outer ring. Our work suggests different formation histories for the galaxy components. Possible origins of the galaxy are discussed, and we conclude that a recent accretion event is the most plausible scenario that accounts for the observational characteristic of PGC 1000714.
Class I methanol masers are found to be good tracers of the interaction between outflows from massive young stellar objects with their surrounding media. Although polarization observations of Class II methanol masers have been able to provide information about magnetic fields close to the central (proto)stars, polarization observations of Class I methanol masers are rare, especially at 44 and 95 GHz. We present the results of linear polarization observations of 39 Class I methanol maser sources at 44 and 95 GHz. These two lines are observed simultaneously with one of the 21 m Korean VLBI Network telescopes in single-dish mode. Approximately 60% of the observed sources have fractional polarizations of a few percent in at least one transition. This is the first reported detection of linear polarization of the 44 GHz methanol maser. The two maser transitions show similar polarization properties, indicating that they trace similar magnetic environments, although the fraction of the linear polarization is slightly higher at 95 GHz. We discuss the association between the directions of polarization angles and outflows. We also discuss some targets having different polarization properties at both lines, including DR21(OH) and G82.58+0.20, which show the 90{\deg} polarization angle flip at 44 GHz.
Closure quantities measured by very long baseline interferometry (VLBI) observations are independent of instrumental and propagation instabilities and antenna gain factors, but are sensitive to source structure. A new method is proposed to calculate a structure index based on the median values of closure quantities rather than the brightness distribution of a source. The results are comparable to structure indices based on imaging observations at other epochs and demonstrate the flexibility of deriving structure indices from exactly the same observations as used for geodetic analysis and without imaging analysis. A three-component model for the structure of source 3C371 is developed by model-fitting closure phases. It provides a real case of tracing how the structure effect identified by closure phases in the same observations as the delay observables affects the geodetic analysis, and investigating which geodetic parameters are corrupted to what extent by the structure effect. Using the resulting structure correction based on the three-component model of source 3C371, two solutions, with and without correcting the structure effect, are made. With corrections, the overall rms of this source is reduced by 1 ps, and the impacts of the structure effect introduced by this single source are up to 1.4 mm on station positions and up to 4.4 microarcseconds on Earth orientation parameters. This study is considered as a starting point for handling the source structure effect on geodetic VLBI from geodetic sessions themselves.
A set of Smoothed Particle Hydrodynamics simulations of the influence of photoionising radiation and stellar winds on a series of 10$^{4}$M$_{\odot}$ turbulent molecular clouds with initial virial ratios of 0.7, 1.1, 1.5, 1.9 and 2.3 and initial mean densities of 136, 1135 and 9096\,cm$^{-3}$ are presented. Reductions in star formation efficiency rates are found to be modest, in the range $30\%-50\%$ and to not vary greatly across the parameter space. In no case was star formation entirely terminated over the $\approx3$\,Myr duration of the simulations. The fractions of material unbound by feedback are in the range $20-60\%$, clouds with the lowest escape velocities being the most strongly affected.\\ Leakage of ionised gas leads to the HII regions rapidly becoming underpressured. The destructive effects of ionisation are thus largely not due to thermally--driven expansion of the HII regions, but to momentum transfer by photoevaporation of fresh material. Our simulations have similar global ionisation rates and we show that the effects of feedback upon them can be adequately modelled as a steady injection of momentum, resembling a momentum--conserving wind.
Are there examples of "astrophysical Russian dolls," and what could we learn from their similarities? In this article, we list a few such examples, including disks, filaments, and clusters. We suggest that forging connections across disciplinary borders enhances our perception of beauty, while simultaneously leading to a more comprehensive understanding of the Universe.
Observations of stars in the the solar vicinity show a clear tendency for old stars to have larger velocity dispersions. This relation is called the age-velocity dispersion relation (AVR) and it is believed to provide insight into the heating history of the Milky Way galaxy. Here, in order to investigate the origin of the AVR, we performed smoothed particle hydrodynamic simulations of the self-gravitating multiphase gas disks in the static disk-halo potentials. Star formation from cold and dense gas is taken into account, and we analyze the evolution of these star particles. We find that exponents of simulated AVR and the ratio of the radial to vertical velocity dispersion are close to the observed values. We also find that the simulated AVR is not a simple consequence of dynamical heating. The evolution tracks of stars with different epochs evolve gradually in the age-velocity dispersion plane as a result of: (1) the decrease in velocity dispersion in star forming regions, and (2) the decrease in the number of cold/dense/gas as scattering sources. These results suggest that the AVR involves not only the heating history of a stellar disk, but also the historical evolution of the ISM in a galaxy.
The fine details of the large-scale structure in the local universe provide important empirical benchmarks for testing cosmological models of structure formation. Dwarf galaxies are key object for such studies. Enlarge the sample of known dwarf galaxies in the local universe. We performed a search for faint, unresolved low-surface brightness dwarf galaxies in the M101 group complex, including the region around the major spiral galaxies M101, M51, and M63 lying at a distance 7.0, 8.6, and 9.0 Mpc, respectively. The new dwarf galaxy sample can be used in a first step to test for significant substructure in the 2D-distribution and in a second step to study the spatial distribution of the galaxy complex. Using filtering algorithms we surveyed 330 square degrees of imaging data obtained from the Sloan Digital Sky Survey. The images were visually inspected. The spatial distribution of known galaxies and candidates was analyzed transforming the system into a M101 eigenframe, using the special geometrical alignment of the group. We discovered 15 new dwarf galaxies and carried out surface photometry in the g and r bands. The similarity of the photometric properties of these dwarfs to those of Local Group dwarfs suggest membership to the M101 group complex. The sky distribution of the candidates follows the thin planar structure outlined by the known members of the three subgroups. The ~3Mpc long filamentary structure has a rms thickness of 72 kpc. The planar structure of the embedded M101 subgroup is even thinner, with rms=49 kpc. The formation of this structure might be due to the expansion of the Local Void to which it borders. Other implications are discussed as well. We show the viability of SDSS data to extend the sample of dwarfs in the local universe and test cosmological models on small scales.
Spectral absorption features can be used to constrain the stellar initial mass function (IMF) in the integrated light of galaxies. Spectral indices used at low redshift are in the far red, and therefore increasingly hard to detect at higher and higher redshifts as they pass out of atmospheric transmission and CCD detector wavelength windows. We employ IMF-sensitive indices at bluer wavelengths. We stack spectra of red, quiescent galaxies around $z=0.4$, from the DEEP2 Galaxy Redshift Survey. The $z=0.4$ red galaxies have 2 Gyr average ages so that they cannot be passively evolving precursors of nearby galaxies. They are slightly enhanced in C and Na, and slightly depressed in Ti. Split by luminosity, the fainter half appears to be older, a result that should be checked with larger samples in the future. We uncover no evidence for IMF evolution between $z=0.4$ and now, but we highlight the importance of sample selection, finding that an SDSS sample culled to select archetypal elliptical galaxies at z$\sim$0 is offset toward a more bottom heavy IMF. Other samples, including our DEEP2 sample, show an offset toward a more spiral galaxy-like IMF. All samples confirm that the reddest galaxies look bottom heavy compared with bluer ones. Sample selection also influences age-color trends: red, luminous galaxies always look old and metal-rich, but the bluer ones can be more metal-poor, the same abundance, or more metal-rich, depending on how they are selected.
Eigenvector one is the formal parameter which allows to introduce some order in the properties of the unobscured type 1 active galaxies. We aim at the understanding of the nature of this parameter, and with this purpose we analyse the most extreme examples of quasars with the highest possible values of the corresponding eigenvalues R_Fe. We selected the appropriate sources from the SDSS and we perform a detailed modelling, including various templates for the Fe II pseudo-continuum and the starlight contribution to the spectrum. Out of 9 sources with the R_Fe larger than 2 selected from the SDSS quasar catalog only one quasar was confirmed to have a high value of R_Fe, equal 4.1. All other sources have R_Fe about 1. The high R_Fe object has an extremely narrow Hbeta line, as in Seyfert 2 galaxies, but the [OIII] in this object is very weak in comparison with Hbeta. Careful reanalysis of a larger sample from SDSS is needed to make stronger conclusions about the properties of the extreme eigenvector 1 sources.
Large-scale shocks formed by clustered feedback of young OB stars are considered an important source of mechanical energy for the ISM and a trigger of molecular cloud formation. Their interaction sites are locations where kinetic energy and magnetic fields are redistributed between ISM phases. In this work we study the effect of the magnetic field on the expansion and fragmentation of supershells and look for the signatures of supershell collisions on dense structures and on the kinetic and magnetic energy distribution of the ISM. We performed a series of high-resolution, three-dimensional simulations of colliding supershells. The shocks are created by time-dependent feedback and evolve in a diffuse turbulent environment that is either unmagnetized or has different initial magnetic field configurations. In the hydrodynamical situation, the expansion law of the superbubbles is consistent with the radius-time relation that is theoretically predicted for wind-blown bubbles. The supershells fragment over their entire surface into small dense clumps that carry more than half of the total kinetic energy in the volume. However, this is not the case when a magnetic field is introduced, either in the direction of the collision or perpendicular to the collision. In magnetized situations, the shell surfaces are more stable to dynamical instabilities. When the magnetic field opposes the collision, the expansion law of the supershells also becomes significantly flatter than in the hydrodynamical case. Although a two-phase medium arises in all cases, in the MHD simulations the cold phase is limited to lower densities.
We present the detection of four far-infrared fine-structure oxygen lines, as well as strong upper limits for the CO(2-1) and [N II] 205 um lines, in 3C 368, a well-studied radio-loud galaxy at z = 1.131. These new oxygen lines, taken in conjunction with previously observed neon and carbon fine-structure lines, suggest a powerful active galactic nucleus (AGN), accompanied by vigorous and extended star formation. A starburst dominated by O8 stars, with an age of ~6.5 Myr, provides a good fit to the fine-structure line data. This estimated age of the starburst makes it nearly concurrent with the latest episode of AGN activity, suggesting a link between the growth of the supermassive black hole and stellar population in this source. We do not detect the CO(2-1) line, down to a level twelve times lower than the expected value for star forming galaxies. This lack of CO line emission is consistent with recent star formation activity if the star-forming molecular gas has low metallicity, is highly fractionated (such that CO is photodissociated through much of the clouds), or is chemically very young (such that CO has not yet had time to form). It is also possible, though we argue unlikely, that the ensemble of fine structure lines are emitted from the region heated by the AGN.
Recent radio observations show that the giant molecular cloud (GMC) mass functions noticeably vary across galactic disks. High-resolution magnetohydrodynamics simulations show that multiple episodes of compression are required for creating a molecular cloud in the magnetized interstellar medium. In this article, we formulate the evolution equation for the GMC mass function to reproduce the observed profiles, for which multiple compression are driven by the network of expanding shells due to HII regions and supernova remnants. We introduce the cloud-cloud collision (CCC) terms in the evolution equation in contrast to the previous work (Inutsuka et al. 2015). The computed time evolution suggests that the GMC mass function slope is governed by the ratio of GMC formation timescale to its dispersal timescale, and that the CCC effect is limited only in the massive-end of the mass function. In addition, we identify a gas resurrection channel that allows the gas dispersed by massive stars to regenerate GMC populations or to accrete onto the pre-existing GMCs. Our results show that almost all of the dispersed gas contribute to the mass growth of pre-existing GMCs in arm regions whereas less than 60 per cent in inter-arm regions. Our results also predict that GMC mass functions have a single power-law exponent in the mass range < 10^5.5 Msun (where Msun represents the solar mass), which is well characterized by GMC self-growth and dispersal timescales. Measurement of the GMC mass function slope provides a powerful method to constrain those GMC timescales and the gas resurrecting factor in various environment across galactic disks.
The globular cluster (GC) system of our Galaxy contains four planetary nebulae (PNe): K 648 (or Ps 1) in M15, IRAS 18333-2357 in M22, JaFu 1 in Pal 6, and JaFu 2 in NGC 6441. Because single-star evolution at the low stellar mass of present-epoch GCs was considered incapable of producing visible PNe, their origin presented a puzzle. We imaged the PN JaFu 1 with the Hubble Space Telescope (HST) to obtain photometry of its central star (CS) and high-resolution morphological information. We imaged IRAS 18333-2357 with better depth and resolution, and we analyzed its archival HST spectra to constrain its CS temperature and luminosity. All PNe in Galactic GCs now have high-quality HST data, allowing us to improve CS mass estimates. We find reasonably consistent masses between 0.53 and 0.58 Msun for all four objects, though estimates vary when adopting different stellar evolutionary calculations. The CS mass of IRAS 18333-2357, though, depends strongly on its temperature, which remains elusive due to reddening uncertainties. For all four objects, we consider their CS and nebular masses, their morphologies, and other incongruities to assess the likelihood that these objects formed from binary stars. Although generally limited by uncertainties (~0.02 Msun) in post-AGB tracks and core mass vs. luminosity relations, the high-mass CS in K 648 indicates a binary origin. The CS of JaFu 1 exhibits compact bright [O III] and Halpha emission, like EGB 6, suggesting a binary companion or disk. Evidence is weaker for a binary origin of JaFu 2.
From numerical simulations, we show that non-rotating magnetohydrodynamic shear flows are unstable to finite amplitude velocity perturbations and become turbulent, leading to the growth and sustenance of magnetic energy, including large scale fields. This supports the concept that sustained magnetic energy from turbulence is independent of the driving mechanism for large enough magnetic Reynolds numbers.
We present a new large-scale (4 square degrees) simultaneous $^{12}$CO, $^{13}$CO, and C$^{18}$O ($J$=1$-$0) mapping of L1188 with the PMO 13.7-m telescope. Our observations have revealed that L1188 consists of two nearly orthogonal filamentary molecular clouds at two clearly separated velocities. Toward the intersection showing large velocity spreads, we find several bridging features connecting the two clouds in velocity, and an open arc structure which exhibits high excitation temperatures, enhanced $^{12}$CO and $^{13}$CO emission, and broad $^{12}$CO line wings. This agrees with the scenario that the two clouds are colliding with each other. The distribution of young stellar object (YSO) candidates implies an enhancement of star formation in the intersection of the two clouds. We suggest that a cloud-cloud collision happened in L1188 about 1~Myr ago, possibly triggering the formation of low- and intermediate-mass YSOs in the intersection.
Ultraluminous X-ray sources (ULXs) are a population of extragalactic objects whose luminosity exceeds the Eddington limit for a 10 Msun black hole (BH). Their properties have been widely interpreted in terms of accreting stellar-mass or intermediate-mass BHs. However at least three neutron stars (NSs) have been recently identified in ULXs through the discovery of periodic pulsations. Motivated by these findings we studied the spectral properties of a sample of bright ULXs using a simple continuum model which was extensively used to fit the X-ray spectra of accreting magnetic NSs in the Galaxy. We found that such a model, consisting of a power-law with a high-energy exponential cut-off, fits very well most of the ULX spectra analyzed here, at a level comparable to that of models involving an accreting BH. On these grounds alone we suggest that other non-pulsating ULXs may host NSs. We found also that above 2 keV the spectrum of known pulsating ULXs is harder than that of the majority of the other ULXs of the sample, with only IC 342 X-1 and Ho IX X-1 displaying spectra of comparable hardness. We thus suggest that these two ULXs may host an accreting NS and encourage searches for periodic pulsations in the flux.
We present near-infrared (0.8-1.8 $\mu$m) spectra of 105 bright (${m_{J}}$ $<$ 10) stars observed with the low resolution spectrometer on the rocket-borne Cosmic Infrared Background Experiment (CIBER). As our observations are performed above the earth's atmosphere, our spectra are free from telluric contamination, which makes them a unique resource for near-infrared spectral calibration. Two-Micron All Sky Survey (2MASS) photometry information is used to identify cross-matched stars after reduction and extraction of the spectra. We identify the spectral types of the observed stars by comparing them with spectral templates from the Infrared Telescope Facility (IRTF) library. All the observed spectra are consistent with late F to M stellar spectral types, and we identify various infrared absorption lines.
The young (~2 Myr) cluster Chamaeleon I is one of the closest laboratories to
study the early stages of star cluster dynamics in a low-density environment.
We studied its structural and kinematical properties combining parameters from
the high-resolution spectroscopic survey Gaia-ESO with data from the
literature. Our main result is the evidence of a large discrepancy between the
velocity dispersion (sigma = 1.14 \pm 0.35 km s^{-1}) of the stellar population
and the dispersion of the pre-stellar cores (~0.3 km s^{-1}) derived from
submillimeter observations. The origin of this discrepancy, which has been
observed in other young star clusters is not clear. It may be due to either the
effect of the magnetic field on the protostars and the filaments, or to the
dynamical evolution of stars driven by two-body interactions. Furthermore, the
analysis of the kinematic properties of the stellar population put in evidence
a significant velocity shift (~1 km s^{-1}) between the two sub-clusters
located around the North and South main clouds. This result further supports a
scenario, where clusters form from the evolution of multiple substructures
rather than from a monolithic collapse.
Using three independent spectroscopic indicators (the gravity indicator
$\gamma$, the equivalent width of the Li line, and the H_alpha 10\% width), we
performed a new membership selection. We found six new cluster members located
in the outer region of the cluster. Starting from the positions and masses of
the cluster members, we derived the level of substructure Q, the surface
density \Sigma and the level of mass segregation $\Lambda_{MSR}$ of the
cluster. The comparison between these structural properties and the results of
N-body simulations suggests that the cluster formed in a low density
environment, in virial equilibrium or supervirial, and highly substructured.
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The relative populations in rotational transitions of CO can be useful for inferring gas conditions and excitation mechanisms at work in the interstellar medium. We present CO emission lines from rotational transitions observed with Herschel/HIFI in the star-forming cores Orion S, Orion KL, Sgr B2(M), and W49N. Integrated line fluxes from these observations are combined with those from Herschel/PACS observations of the same sources to construct CO spectral line energy distributions (SLEDs) from $5\leq J_u\leq48$. These CO SLEDs are compared to those reported in other galaxies, with the intention of empirically determining which mechanisms dominate excitation in such systems. We find that CO SLEDs in Galactic star-forming cores cannot be used to reproduce those observed in other galaxies, although the discrepancies arise primarily as a result of beam filling factors. The much larger regions sampled by the Herschel beams at distances of several Mpc contain significant amounts of cooler gas which dominate the extragalactic CO SLEDs, in contrast to observations of Galactic star-forming regions which are focused specifically on cores containing primarily hot molecular gas.
Albeit radial migration must be a ubiquitous process in disk galaxies, its significance in the evolution of stellar discs is not always reflected through global simple trends (e.g. a single abundance curve). However, there are other key observables, such as the metallicity distribution function (MDF), that may shed some light in this matter. We argue that the shape of the MDF not only tells us whether the stellar disc experienced radial migration, but it also contains important clues on the structure that triggered it. Specifically, the MDF contains information about the dynamics and morphology of the spiral pattern (e.g. pitch angle, pattern speed). In order to constrain the spiral parameters, we have included a detailed recipe for the chemical tagging in our simulations; this allows us to produce a restriction of the structural parameters of the spiral arms in the Milky Way as well as a method to constrain chemical evolution models towards the center of the Galactic disc, where no chemical model provides information. We also show that a stellar disc that has evolved dynamically and chemically can preserve a global metallicity gradient despite of having suffered important heating and radial migration; this means that the presence of a metallicity gradient in a given galaxy, does not guarantee that radial mixing has not played a role in the evolution of the galaxy.
Among the most important goals in cosmology is detecting and quantifying small ($M_\mathrm{halo}\simeq10^{6-9}\,\mathrm{M}_\odot$) dark matter (DM) subhalos. Current probes around the Milky Way (MW) are most sensitive to such substructure within $\sim20$~kpc of the halo center, where the galaxy contributes significantly to the potential. We explore the effects of baryons on subhalo populations in $\Lambda$CDM using cosmological zoom-in baryonic simulations of MW-mass halos from the Latte simulation suite, part of the Feedback In Realistic Environments (FIRE) project. Specifically, we compare simulations of the same two halos run using (1) DM-only (DMO), (2) full baryonic physics, and (3) DM with an embedded disk potential grown to match the FIRE simulation. Relative to baryonic simulations, DMO simulations contain $\sim2\times$ as many subhalos within 100 kpc of halo center; this excess is $\gtrsim5\times$ within 25 kpc. At $z=0$, the baryonic simulations are completely devoid of subhalos down to $3\times10^6\,\mathrm{M}_\odot$ within $15$ kpc of the MW-mass galaxy. Despite the complexities of baryonic physics, the simple addition of an embedded central disk potential to DMO simulations reproduces this subhalo depletion, including trends with radius, remarkably well. Thus, the additional tidal field from the central galaxy is the primary cause of subhalo depletion. Subhalos on radial orbits that pass close to the central galaxy are preferentially destroyed, causing the surviving subhalo population to have tangentially biased orbits compared to DMO predictions. Our method of embedding a disk potential in DMO simulations provides a fast and accurate alternative to full baryonic simulations, thus enabling suites of cosmological simulations that can provide accurate and statistical predictions of substructure populations.
Distant galaxies encapsulate the various stages of galaxy evolution and
formation from over 95% of the development of the universe. As early as
twenty-five years ago, little was known about them, however since the first
systematic survey was completed in the 1990s, increasing amounts of resources
have been devoted to their discovery and research. This book summarises for the
first time the numerous techniques used for observing, analysing, and
understanding the evolution and formation of these distant galaxies.
In this rapidly expanding research field, this text is an every-day companion
handbook for graduate students and active researchers. It provides guidelines
in sample selection, imaging, integrated spectroscopy and 3D spectroscopy,
which help to avoid the numerous pitfalls of observational and analysis
techniques in use in extragalactic astronomy. It also paves the way for
establishing relations between fundamental properties of distant galaxies. At
each step, the reader is assisted with numerous practical examples and
ready-to-use methodology to help understand and analyse research.
We examine the optical photometric and polarimetric variability of the luminous type 1 non-blazar quasar 3C 323.1 (PG 1545+210). Two optical spectro-polarimetric measurements taken during the periods 1996$-$98 and 2003 combined with a $V$-band imaging polarimetric measurement taken in 2002 reveal that (1) as noted in the literature, the polarization of 3C 323.1 is confined only to the continuum emission, that is, the emission from the broad line region is unpolarized; (2) the polarized flux spectra show evidence of a time-variable broad absorption feature in the wavelength range of the Balmer continuum and other recombination lines; (3) weak variability in the polarization position angle ($PA$) of $\sim$ 4 deg over a time-scale of 4$-$6 years is observed; and (4) the V-band total flux and the polarized flux show highly correlated variability over a time-scale of one year. Taking the above-mentioned photometric and polarimetric variability properties and the results from previous studies into consideration, we propose a geometrical model for the polarization source in 3C 323.1, in which an equatorial absorbing region and an axi-asymmetric equatorial electron-scattering region are assumed to be located between the accretion disc and the broad line region. The scattering/absorbing regions can perhaps be attributed to the accretion disc wind or flared disc surface, but further polarimetric monitoring observations for 3C~323.1 and other quasars with continuum-confined polarization are needed to probe the true physical origins of these regions.
Detailed chemical abundances of two stars in the intermediate-age Large Magellanic Cloud (LMC) globular cluster NGC~1718 are presented, based on high resolution spectroscopic observations with the MIKE spectrograph. The detailed abundances confirm NGC~1718 to be a fairly metal-rich cluster, with an average [Fe/H] ~ -0.55+/-0.01. The two red giants appear to have primordial O, Na, Mg, and Al abundances, with no convincing signs of a composition difference between the two stars---hence, based on these two stars, NGC~1718 shows no evidence for hosting multiple populations. The Mg abundance is lower than Milky Way field stars, but is similar to LMC field stars at the same metallicity. The previous claims of very low [Mg/Fe] in NGC~1718 are therefore not supported in this study. Other abundances (Si, Ca, Ti, V, Mn, Ni, Cu, Rb, Y, Zr, La, and Eu) all follow the LMC field star trend, demonstrating yet again that (for most elements) globular clusters trace the abundances of their host galaxy's field stars. Similar to the field stars, NGC~1718 is found to be mildly deficient in explosive $\alpha$-elements, but moderately to strongly deficient in O, Na, Mg, Al, and Cu, elements which form during hydrostatic burning in massive stars. NGC~1718 is also enhanced in La, suggesting that it was enriched in ejecta from metal-poor AGB stars.
We describe the structural, stellar population and gas properties of the nearest Ultra Diffuse Galaxy (UDG) discovered so far: UGC2162 (z=0.00392; R$_{e,g}$=1.7$(\pm$0.2) kpc; $\mu_g(0)$=24.4$\pm$0.1 mag/arcsec$^2$; g i=0.33$\pm$0.02). This galaxy, located at a distance of 12.3($\pm$1.7) Mpc, is a member of the M77 group. UGC2162 has a stellar mass of $\sim$2($^{+2}_{-1}$)$\times$10$^7$ M$_\odot$ and is embedded within a cloud of HI gas $\sim$10 times more massive: $\sim$1.9($\pm$0.6)$\times$10$^8$ M$_\odot$. Using the width of its HI line as a dynamical proxy, the enclosed mass within the inner R$\sim$5 kpc is $\sim$4.6($\pm$0.8)$\times$10$^9$ M$_\odot$ (i.e. M/L$\sim$200). The estimated virial mass from the cumulative mass curve is $\sim$8($\pm$2)$\times$10$^{10}$ M$_\odot$. Ultra deep imaging from the IAC Stripe82 Legacy Project show that the galaxy is irregular and has many star forming knots, with a gas-phase metallicity around 1/3 the solar value. Its estimated Star Formation Rate (SFR) is $\sim$0.01 M$_\odot$/yr. This SFR would double the stellar mass of the object in $\sim$2 Gyr. If the object were to stop forming stars at this moment, after a passive evolution, its surface brightness would become extremely faint: $\mu_g(0)$$\sim$27 mag/arcsec$^2$ and its size would remain large R$_{e,g}$$\sim$ 1.8 kpc. Such faintness would make it almost undetectable to most present-day surveys. This suggests that there could be an important population of M$_{\star}$$\sim$10$^7$ M$_\odot$ "dark galaxies" in rich environments (depleted of HI gas) waiting to be discovered by current and future ultra-deep surveys.
(abridged) In this paper we revisit the problem of inferring the innermost structure of the Milky Way's nuclear star cluster via star counts, to clarify whether it displays a core or a cusp around the central black hole. Through image stacking and improved PSF fitting we push the completeness limit about one magnitude deeper than in previous, comparable work. Contrary to previous work, we analyse the stellar density in well-defined magnitude ranges in order to be able to constrain stellar masses and ages. The RC and brighter giant stars display a core-like surface density profile within a projected radius R<0.3 pc of the central black hole, in agreement with previous studies, but show a cusp-like surface density distribution at larger R. The surface density of the fainter stars can be described well by a single power-law at R<2 pc. The cusp-like profile of the faint stars persists even if we take into account the possible contamination of stars in this brightness range by young pre-main sequence stars. The data are inconsistent with a core-profile for the faint stars.Finally, we show that a 3D Nuker law provides a very good description of the cluster structure. We conclude that the observed stellar density at the Galactic Centre, as it can be inferred with current instruments, is consistent with the existence of a stellar cusp around the Milky Way's central black hole, Sgr A*. This cusp is well developed inside the influence radius of about 3 pc of Sgr A* and can be described by a single three-dimensional power-law with an exponent gamma=1.23+-0.05. The apparent lack of RC stars and brighter giants at projected distances of R < 0.3 pc (R<8") of the massive black hole may indicate that some mechanism has altered their distribution or intrinsic luminosity.
This is the second of three papers that search for the predicted stellar cusp around the Milky Way's central black hole, Sagittarius A*, with new data and methods.We use adaptive optics assisted high angular resolution images obtained with the NACO instrument at the ESO VLT. Through optimised PSF fitting we remove the light from all detected stars above a given magnitude limit. Subsequently we analyse the remaining, diffuse light density. The azimuthally averaged surface light density profile within a projected distance of R0.5 pc from Sagittarius A* can be described consistently by a single power law with an exponent of Gamma=0.28+-0.03, similar to what has been found for the surface number density of faint stars in Paper I. The analysed diffuse light arises from sub-giant and main-sequence stars with K=19-20 with masses of 1-2 Msol. These stars can be old enough to be dynamically relaxed. The observed power-law profile and its slope are consistent with the existence of a relaxed stellar cusp around the Milky Way's central black hole. We find that a Nuker law provides an adequate description of the nuclear cluster's intrinsic shape (assuming spherical symmetry). The 3D power-law slope near SgrA* is gamma=1.23+-0.05. The stellar density decreases more steeply beyond a break radius of about 3 pc, which corresponds roughly to the radius of influence of the massive black hole. At a distance of 0.01 pc from the black hole, we estimate a stellar mass density of 2.3+-0.3x1e7 Msol pc(-3) and a total enclosed stellar mass of 180+-20 Msol.
The distribution of stars around a massive black hole (MBH) has been addressed in stellar dynamics for the last four decades by a number of authors. Due to its proximity, the centre of the Milky Way is the only observational test case where the stellar distribution can be accurately tested. Past observational work indicated that the brightest giants in the Galactic Centre (GC) may show a density deficit around the central black hole, not a cusp-like distribution, while we theoretically expect the presence of a stellar cusp. In this work we present a solution to this long-standing problem. We perform direct-summation $N-$body simulations of star clusters around massive black holes and compare the results of our simulations with new observational data of the GC's nuclear cluster. We find that after a Hubble time, the distribution of bright stars as well as the diffuse light follow power-law distributions in projection with slopes of $\Gamma \approx -0.3$ in our simulations. This is in excellent agreement with what is seen in star counts and in the distribution of the diffuse stellar light extracted from adaptive optics (AO) assisted near infrared observations of the GC. Our simulations also confirm that there exists a missing giant star population within a projected radius of a few arcsec around Sgr A*. Such a depletion of giant stars in the innermost 0.1 pc could be explained by a previously present gaseous disc and collisions, which means that a stellar cusp would also be present at the innermost radii, but in the form of degenerate compact cores.
We explore the effect of using different kinematic tracers (HI and H$\alpha$) on reconstructing the encounter parameters of the Mice major galaxy merger (NGC 4676A/B). We observed the Mice using the SparsePak Integral Field Unit (IFU) on the WYIN telescope, and compared the H$\alpha$ velocity map with VLA HI observations. The relatively high spectral resolution of our data (R $\approx$ 5000) allows us to resolve more than one kinematic component in H$\alpha$ emission line of some of the fibers. We separate the H$\alpha$ emission of the star forming regions from that of shock-heated regions based on the [N II]/H$\alpha$ line ratio and the velocity dispersion of the components. We show that the kinematics of star-forming regions agree with that of the cold gas (HI), particularly in the tidal tails of the system. We put constraints the encounter parameters of the Mice by matching the morphology and kinematics of these tidal tails with an equal-mass galaxy merger simulation. We use an automated modeling method based on the Identikit software package. In our method, we quantify the goodness of the match and the uncertainty of the resulting encounter parameters. Most of the initial conditions reconstructed using H$\alpha$ and HI kinematics are consistent within the estimated uncertainty, and qualitatively agree with the results of previous works based on visual matching techniques. For example, we find 210$\pm^{50}_{40}$ Myrs, and 180$\pm^{50}_{40}$ Myrs for the time since pericenter, when modeling H$\alpha$ and HI kinematics, respectively. This confirms that in some cases, H$\alpha$ kinematics can be used instead of HI kinematics for reconstructing the initial conditions of galaxy mergers, and our automated modeling method is applicable to some merging systems.
We have derived exact axisymmetric solutions of the two-dimensional Lane-Emden equations with rotation. These solutions are intrinsically favored by the differential equations regardless of any adopted boundary conditions and the physical solutions of the Cauchy problem are bound to oscillate about and remain close to these intrinsic solutions. The isothermal solutions are described by power-law density profiles in the radial direction, whereas the polytropic solutions are described by radial density profiles that are powers of the zeroth-order Bessel function of the first kind. Both families of solutions decay exponentially in the vertical direction and both result in increasing or nearly flat radial rotation curves. The results are applicable to gaseous spiral-galaxy disks that exhibit flat rotation curves and to the early stages of protoplanetary disk formation before the central star is formed.
We derive relations between the effective radii $R_{\mathrm{eff}}$ of galaxies and the virial radii $R_{200c}$ of their dark-matter halos over the redshift range $0 < z < 3$. For galaxies, we use the measured sizes from deep images taken with Hubble Space Telescope for the CANDELS program; for halos, we use the inferred sizes from abundance matching to cosmological dark-matter simulations via a stellar mass--halo mass (SMHM) relation. For this purpose, we derive a new SMHM relation based on the same selection criteria and other assumptions as for our sample of galaxies with size measurements. As a check on the robustness of our results, we also derive $R_{\mathrm{eff}}$--$R_{200c}$ relations for three independent SMHM relations from the literature. We find that galaxy $R_{\mathrm{eff}}$ is proportional on average to halo $R_{200c}$, confirming and extending to high redshifts the $z=0$ results of Kravtsov (2013). Late-type galaxies (with low S\'ersic index and high specific star formation rate, sSFR) follow a linear $R_{\mathrm{eff}}$--$R_{200c}$ relation, with effective sizes at $1 < z < 3$ close to those predicted by simple models of disk formation; at $0 < z < 1$, the sizes of late-type galaxies are slightly ($\sim 0.2$ dex) below this prediction. Early-type galaxies (with high S\'ersic index and low sSFR) follow a roughly parallel $R_{\mathrm{eff}}$--$R_{200c}$ relation, $\sim$ 0.2--0.3 dex below the one for late-type galaxies. Our observational results, reinforced by recent hydrodynamical simulations, indicate that galaxies grow quasi-homologously with their dark-matter halos.
The observation and imaging of hundreds or thousands of radio sources with the technique of very long baseline interferometry (VLBI) is a computationally intensive task. However, these surveys allow us to conduct statistical investigations of large source samples, and also to discover new phenomena or types of objects. The field of view of these high-resolution VLBI imaging observations is typically a few arcseconds at cm wavelengths. For practical reasons, often a much smaller fraction of the field, the central region is imaged only. With an automated process we imaged the ~1.5-arcsec radius fields around more than 1000 radio sources, and found a variety of extended radio structures. Some of them are yet unknown in the literature.
Methanol (CH$_3$OH) is found to be abundant and widespread towards the Central Molecular Zone, the inner few hundred parsecs of our Galaxy. Its origin is, however, not fully understood. It was proposed that the high cosmic ray ionisation rate in this region could lead to a more efficient non-thermal desorption of this species formed on grain surfaces, but it would also mean that this species is destroyed in a relatively short timescale. In a first step, we run chemical models with a high cosmic ray ionisation rate and find that this scenario can only reproduce the lowest abundances of methanol derived in this region ($\sim$10$^{-9}$-10$^{-8}$). In a second step, we investigate another scenario based on episodic explosions of grain mantles. We find a good agreement between the predicted abundances of methanol and the observations. We find that the dominant route for the formation of methanol is through hydrogenation of CO on the grains followed by the desorption due to the grain mantle explosion. The cyclic aspect of this model can explain the widespread presence of methanol without requiring any additional mechanism. We also model silicon monoxide (SiO), another species detected in several molecular clouds of the Galactic Centre. An agreement is found with observations for a high depletion of Si (Si/H $\sim$ 10$^{-8}$) with respect to the solar abundance.
Context. The combination of wideband receivers and spectrometers currently available in (sub-)millimeter observatories deliver wide- field hyperspectral imaging of the interstellar medium. Tens of spectral lines can be observed over degree wide fields in about fifty hours. This wealth of data calls for restating the physical questions about the interstellar medium in statistical terms. Aims. We aim at gaining information on the physical structure of the interstellar medium from a statistical analysis of many lines from different species over a large field of view, without requiring detailed radiative transfer or astrochemical modeling. Methods. We coupled a nonlinear rescaling of the data with one of the simplest multivariate analysis methods, namely the Principal Component Analysis, to decompose the observed signal into components that we interpret first qualitatively and then quantitatively based on our deep knowledge of the observed region and of the astrochemistry at play. Results. We identify 3 principal components, linear compositions of line brightness temperatures, that are correlated at various levels with the column density, the volume density and the UV radiation field. Conclusions. When sampling a sufficiently diverse mixture of physical parameters, it is possible to decompose the molecular emission in order to gain physical insight on the observed interstellar medium. This opens a new avenue for future studies of the interstellar medium.
In the BHR71 region, two low-mass protostars drive two distinguishable outflows. They constitute an ideal laboratory to investigate the effects of shock chemistry and the mechanisms that led to their formation. We aim to define the morphology of the warm gas component of the BHR 71 outflow and at modelling its shocked component. We present the first far infrared Herschel images of the BHR71 outflow in the CO(14-13), H$_2$O (2$_{21}$-1$_{10}$), H$_2$O (2$_{12}$-1$_{01}$) and [OI] 145 $\mu$m, lines, revealing the presence of several knots of warm, shocked gas associated with fast outflowing gas. In two of these knots we performed a detailed study of the physical conditions by comparing a large set of transitions from several molecules to a grid of shock models. Herschel lines ratios in the outflow knots are quite similar, showing that the excitation conditions of the fast moving gas do not change significantly within the first $\sim$ 0.068 pc of the outflow, apart at the extremity of the southern blue-shifted lobe that is expanding outside the molecular cloud. Rotational diagram, spectral line profile and LVG analysis of the CO lines in knot A show the presence of two gas components: one extended, cold ($T\sim$80 K) and dense ($n$(H$_2$) = 3$\times$10$^5$-4$\times$10$^6$ cm$^{-3}$) and another compact (18 arcsec), warm ($T$ = 1700-2200 K) with slightly lower density ($n$(H$_2$) = (2-6)$\times$10$^4$ cm$^{-3}$). In the two brightest knots (where we performed shock modelling) we found that H$_2$ and CO are well fitted with non-stationary (young) shocks. These models, however, significantly underestimate the observed fluxes of [OI] and OH lines, but are not too far off those of H$_2$O, calling for an additional, possibly dissociative, J-type shock component. Our modelling indirectly suggests that an additional shock component exists, possibly a remnant of the primary jet
We analyse new optical observations of the gravitational lens system SDSS J1515+1511. These include a 2.6-year photometric monitoring with the Liverpool Telescope (LT) in the $r$ band, as well as a spectroscopic follow-up with the LT and the Gran Telescopio Canarias (GTC). Our $r$-band LT light curves cover a quiescent microlensing period of the doubly imaged quasar at $z_{\rm s}$ = 2.049, which permits us to robustly estimate the time delay between the two images A and B: 211 $\pm$ 5 days (1$\sigma$ confidence interval; A is leading). Unfortunately, the main lensing galaxy (G1) is so faint and close to the bright quasar that it is not feasible to accurately extract its spectrum through the GTC data. However, assuming the putative redshift $z_{\rm G1}$ = 0.742, the GTC and LT spectra of the distant quasar are used to discuss the macrolens magnification, and the extinction and microlensing effects in G1. The new constraints on the time delay and macrolens magnification ratio essentially do not change previous findings on the mass scale of G1 and external shear, while the redshift of the lensing mass is found to be consistent with the assumed value of $z_{\rm G1}$. This is a clear evidence that G1 is indeed located at $z_{\rm G1}$ = 0.742. From the GTC data we also obtain the redshift of two additional objects (the secondary galaxy G2 and a new absorption system) and discuss their possible role in the lens scenario.
We report results of a spectroscopic campaign carried out at the 10 m Gran Telescopio Canarias for a sample of 22 BL Lac objects detected (or candidates) at TeV energies, aimed to determine or constrain their redshift. This is of fundamental importance for the interpretation of their emission models, for population studies and also mandatory to study the interaction of high energy photons with the extragalactic background light using TeV sources. High signal-to-noise optical spectra in the range 4250 - 10000 {\AA} were obtained to search for faint emission and/or absorption lines from both the host galaxy or the nucleus. We determine a new redshift for PKS 1424+240 (z = 0.604) and a tentative one for 1ES 0033+595 (z = 0.467). We are able to set new spectroscopic redshift lower limits for other three sources on the basis of Mg II and Ca II intervening absorption features: BZB J1243+3627 (z > 0.483), BZB J1540+8155 (z > 0.672), and BZB 0J2323+4210 (z > 0.267). We confirm previous redshift estimates for four blazars: S3 0218+357 (z = 0.944), 1ES 1215+303 (z = 0.129), W Comae (z = 0.102), and MS 1221.8+2452 (z = 0.218). For the remaining targets, in seven cases (S2 0109+22, 3C 66A, VER J0521+211, S4 0954+65, BZB J1120+4214, S3 1227+25, BZB J2323+4210), we do not validate the proposed redshift. Finally for all sources of still unknown redshift, we set a lower limit based on the minimum equivalent width of absorption features expected from the host galaxy.
Recently, Hoang et al. (arXiv:1608.05284) reported analysis of the interaction of relativistic spacecrafts with interstellar medium (ISM, i.e. gas atoms and dust particles) relevant for the Breakthrough starshot initiative (https://breakthroughinitiatives.org/Initiative/3). The main conclusion is that dust pose much greater threat to the starship than gas atoms. However, analysis used to treat interaction of the spaceship with gas atoms is based on the incorrect use of the Szenes model. Only by proper treatment of the Szenes model can be found if the conclusion remains valid - or not. In the following, the main comments we have raised about the paper are listed. Present text is based on the v2 version of the above mentioned paper [0] that was accepted for publication in Astophysical Journal.
We present a low-frequency view of the Perseus cluster with new observations from the Karl G. Jansky Very Large Array (JVLA) at 230-470 MHz. The data reveal a multitude of new structures associated with the mini-halo. The mini-halo seems to be influenced both by the AGN activity as well as by the sloshing motion of the cool core cluster's gas. In addition, it has a filamentary structure similar to that seen in radio relics found in merging clusters. We present a detailed description of the data reduction and imaging process of the dataset. The depth and resolution of the observations allow us to conduct for the first time a detailed comparison of the mini-halo structure with the X-ray structure as seen in the Chandra X-ray images. The resulting image shows very clearly that the mini-halo emission is mostly contained behind the cold fronts, similar to that predicted by simulations of gas sloshing in galaxy clusters. However, due to the proximity of the Perseus cluster, as well as the quality of the data at low radio frequencies and at X-ray wavelengths, we also find evidence of fine structure. This structure includes several radial radio filaments extending in different directions, a concave radio structure associated with the southern X-ray bay and sharp edges that correlate with X-ray edges. Mini-halos are therefore not simply diffuse, uniform radio sources, but are rather filled with a rich variety of complex structures. These results illustrate the high-quality images that can be obtained with the new JVLA at low radio-frequencies, as well as the necessity to obtain deeper, higher-fidelity radio images of mini-halos and halos in clusters to further understand their origin.
To investigate the relationship between thermal and non-thermal components in merger galaxy clusters, we present deep JVLA and Chandra observations of the HST Frontier Fields cluster MACS J0717.5+3745. The Chandra image shows a complex merger event, with at least four components belonging to different merging subclusters. NW of the cluster, $\sim 0.7$ Mpc from the center, there is a ram-pressure-stripped core that appears to have traversed the densest parts of the cluster after entering the ICM from the direction of a galaxy filament to the SE. We detect a density discontinuity NNE of this core which we speculate is associated with a cold front. Our radio images reveal new details for the complex radio relic and radio halo in this cluster. In addition, we discover several new filamentary radio sources with sizes of 100-300 kpc. A few of these seem to be connected to the main radio relic, while others are either embedded within the radio halo or projected onto it. A narrow-angled-tailed (NAT) radio galaxy, a cluster member, is located at the center of the radio relic. The steep spectrum tails of this AGN leads into the large radio relic where the radio spectrum flattens again. This morphological connection between the NAT radio galaxy and relic provides evidence for re-acceleration (revival) of fossil electrons. The presence of hot $\gtrsim 20$ keV ICM gas detected by Chandra near the relic location provides additional support for this re-acceleration scenario.
A revolution in galaxy cluster science is only a few years away. The survey machines eROSITA and Euclid will provide cluster samples of never-before-seen statistical quality. XMM-Newton will be the key instrument to exploit these rich datasets in terms of detailed follow-up of the cluster hot gas content, systematically characterizing sub-samples as well as exotic new objects.
In a survey conducted between 2011-12 of interstellar Na I D line profiles in the direction of the Vela supernova remnant, a few lines of sight showed dramatic changes in low velocity absorption components with respect to profiles from 1993-1994 reported by Cha & Sembach. Three stars - HD 63578, HD 68217 and HD 76161 showed large decrease in strength over the 1993-2012 interval. HD 68217 and HD 76161 are associated with the Vela SNR whereas HD 63578 is associated with $\gamma^2$ Velorum wind bubble. Here, we present high spectral resolution observations of Ca II K lines obtained with the Southern African Large Telescope (SALT) towards these three stars along with simultaneous observations of Na I D lines. These new spectra confirm that the Na D interstellar absorption weakened drastically between 1993-1994 and 2011-2012 but show for the first time that the Ca II K line is unchanged between 1993-1994 and 2015. This remarkable contrast between the behaviour of Na D and Ca II K line absorption lines is a puzzle concerning gas presumably affected by the outflow from the SNR and the wind from $\gamma^2$ Velorum.
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We use EAGLE to explore the effect galaxy mergers have on the stellar specific angular momentum of galaxies, $j_{\rm stars}$. We characterise mergers into: dry (gas-poor)/wet (gas-rich), major/minor, and by different spin alignments and orbital parameters. Our wet (dry) mergers have an average neutral gas fraction (i.e. the ratio between the neutral gas and the stellar masses of the merging system) of $1.1$ ($0.02$), while minor (major) mergers are those with stellar mass ratios between the secondary and primary galaxy in the range $0.1-0.3$ ($\ge 0.3$). We correlate the positions of galaxies in the $j_{\rm stars}$-stellar mass plane at $z=0$ with their merger history, and find that galaxies of low spins suffered dry mergers, while galaxies of normal/high spins suffered predominantly wet mergers, if any at all. The radial $j_{\rm stars}$ profiles of galaxies that went through dry mergers are deficient by $\approx 0.3$~dex at $r\lesssim 10\,r_{50}$ compared to galaxies that went through wet mergers. By studying galaxies before and after mergers, we find that dry mergers reduce $j_{\rm stars}$ by $\approx 30$%, while wet mergers increase it by $\approx 10$%, on average. The latter is connected to the build-up of the central stellar over-density by newly formed stars of high rotational speed. Moving from minor to major mergers mostly accentuates the effects above. When the spin vectors of the galaxies prior to the dry merger are misaligned, $j_{\rm stars}$ decreases to a greater magnitude, while in wet mergers, co-rotation and high orbital angular momentum lead to the largest $j_{\rm stars}$ increase. We make predictions for what would be the observational signatures in the mean $j_{\rm stars}$ profiles driven by dry mergers: (i) shallow radial profiles and (ii) profiles that continue to rise beyond $\approx 10\,r_{50}$, both of which are significantly different from spiral galaxies.
We explore for the first time the effect of self-interacting dark matter (SIDM) on the dark matter (DM) and baryonic distribution in massive galaxies formed in hydrodynamical cosmological simulations, including explicit baryonic physics treatment. A novel implementation of Super-Massive Black Hole (SMBH) formation and evolution is used, as in Tremmel et al.(2015, 2016), allowing to explicitly follow SMBH dynamics at the center of galaxies. A high SIDM constant cross-section is chosen, $\sigma$=10 $\rm cm^2/gr$, to amplify differences from CDM models. Milky Way-like galaxies form a shallower DM density profile in SIDM than they do in CDM, with differences already at 20 kpc scales. This demonstrates that even for the most massive spirals the effect of SIDM dominates over the adiabatic contraction due to baryons. Strikingly, the dynamics of SMBHs differs in the SIDM and reference CDM case. SMBHs in massive spirals have sunk to the centre of their host galaxy in both the SIDM and CDM run, while in less massive galaxies about 80$\%$ of the SMBH population is off-centered in the SIDM case, as opposed to the CDM case in which $\sim$90$\%$ of SMBHs have reached their host's centre. SMBHs are found as far as $\sim$9 kpc away from the centre of their host SIDM galaxy. This difference is due to the increased dynamical friction timescale caused by the lower DM density in SIDM galaxies compared to CDM, resulting in 'core stalling'. This pilot work highlights the importance of simulating in a full hydrodynamical context different DM models combined to SMBH physics to study their influence on galaxy formation.
We present a new method to derive oxygen and carbon abundances using the ultraviolet (UV) lines emitted by the gas-phase ionised by massive stars. The method is based on the comparison of the nebular emission-line ratios with those predicted by a large grid of photo-ionisation models. Given the large dispersion in the O/H - C/O plane, our method firstly fixes C/O using ratios of appropriate emission lines and, in a second step, calculates O/H and the ionisation parameter from carbon lines in the UV. We find abundances totally consistent with those provided by the direct method when we apply this method to a sample of objects with an empirical determination of the electron temperature using optical emission lines. The proposed methodology appears as a powerful tool for systematic studies of nebular abundances in star-forming galaxies at high redshift.
We investigate how star formation efficiency can be significantly decreased by the removal of a molecular cloud's envelope by feedback from an external source. Feedback from star formation has difficulties halting the process in dense gas but can easily remove the less dense and warmer envelopes where star formation does not occur. However, the envelopes can play an important role keeping their host clouds bound by deepening the gravitational potential and providing a constraining pressure boundary. We use numerical simulations to show that removal of the cloud envelopes results in all cases in a fall in the star formation efficiency (SFE). At 1.38 free-fall times our 4 pc cloud simulation experienced a drop in the SFE from 16 to six percent, while our 5 pc cloud fell from 27 to 16 per cent. At the same time, our 3 pc cloud (the least bound) fell from an SFE of 5.67 per cent to zero when the envelope was lost. The star formation efficiency per free-fall time varied from zero to $\approx$ 0.25 according to $\alpha$, defined to be the ratio of the kinetic plus thermal to gravitational energy, and irrespective of the absolute star forming mass available. Furthermore the fall in SFE associated with the loss of the envelope is found to even occur at later times. We conclude that the SFE will always fall should a star forming cloud lose its envelope due to stellar feedback, with less bound clouds suffering the greatest decrease.
Deep observations are revealing a growing number of young galaxies in the first billion year of cosmic time. Compared to typical galaxies at later times, they show more extreme emission-line properties, higher star formation rates, lower masses, and smaller sizes. However, their faintness precludes studies of their chemical abundances and ionization conditions, strongly limiting our understanding of the physics driving early galaxy build-up and metal enrichment. Here we study a rare population of UV-selected, sub$-L^{*}$(z=3) galaxies at redshift 2.4$<z<$3.5 that exhibit all the rest-frame properties expected from primeval galaxies. These low-mass, highly-compact systems are rapidly-forming galaxies able to double their stellar mass in only few tens million years. They are characterized by very blue UV spectra with weak absorption features and bright nebular emission lines, which imply hard radiation fields from young hot massive stars. Their highly-ionized gas phase has strongly sub-solar carbon and oxygen abundances, with metallicities more than a factor of two lower than that found in typical galaxies of similar mass and star formation rate at $z\lesssim$2.5. These young galaxies reveal an early and short stage in the assembly of their galactic structures and their chemical evolution, a vigorous phase which is likely to be dominated by the effects of gas-rich mergers, accretion of metal-poor gas and strong outflows.
We present the discovery and spectrophotometric characterization of a large sample of 164 faint ($i_{AB}$ $\sim$ $23$-$25$ mag) star-forming dwarf galaxies (SFDGs) at redshift $0.13$ $\leq z \leq$ $0.88$ selected by the presence of bright optical emission lines in the VIMOS Ultra Deep Survey (VUDS). We investigate their integrated physical properties and ionization conditions, which are used to discuss the low-mass end of the mass-metallicity relation (MZR) and other key scaling relations. We use optical VUDS spectra in the COSMOS, VVDS-02h, and ECDF-S fields, as well as deep multiwavelength photometry, to derive stellar masses, star formation rates (SFR) and gas-phase metallicities. The VUDS SFDGs are compact (median $r_{e}$ $\sim$ $1.2$ kpc), low-mass ($M_{*}$ $\sim$ $10^7-10^9$ $M_{\odot}$) galaxies with a wide range of star formation rates (SFR($H\alpha$) $\sim 10^{-3}-10^{1}$ $M_{\odot}/yr$) and morphologies. Overall, they show a broad range of subsolar metallicities (12+log(O/H)=$7.26$-$8.7$; $0.04$ $\lesssim Z/Z_{\odot} \lesssim$ $1$). The MZR of SFDGs shows a flatter slope compared to previous studies of galaxies in the same mass range and redshift. We find the scatter of the MZR partly explained in the low mass range by varying specific SFRs and gas fractions amongst the galaxies in our sample. Compared with simple chemical evolution models we find that most SFDGs do not follow the predictions of a "closed-box" model, but those from a gas regulating model in which gas flows are considered. While strong stellar feedback may produce large-scale outflows favoring the cessation of vigorous star formation and promoting the removal of metals, younger and more metal-poor dwarfs may have recently accreted large amounts of fresh, very metal-poor gas, that is used to fuel current star formation.
We present the deep and wide $V$ and $I_c$ photometry of the Sextans dwarf spheroidal galaxy (dSph) taken by Suprime-Cam imager on the Subaru Telescope, which extends out to the tidal radius. The colour-magnitude diagram (CMD) reaches two magnitudes below the main sequence (MS) turn-off, showing a steep red giant branch, blue and red horizontal branch (HB), sub-giant branch (SGB), MS, and blue stragglers (BS). We construct the radial profile of each evolutionary phase and demonstrate that blue HB stars are more spatially extended, while red HB stars are more centrally concentrated than the other components. The colour distribution of SGB stars also varies with the galactocentric distance; the inner SGB stars shift bluer than those in the outskirt. The radial differences in the CMD morphology indicate the existence of the age gradient. The relatively younger stars ($\sim10$ Gyr) are more centrally concentrated than the older ones ($\sim13$ Gyr). The spatial contour maps of stars in different age bins also show that the younger population has higher concentration and higher ellipticity than the older one. We also detect the centrally concentrated bright BS stars, the number of which is consistent with the idea that a part of these stars belongs to the remnant of a disrupted star cluster discovered in the previous spectroscopic studies.
Broad emission-line outflows of active galactic nuclei (AGNs) have been proposed for many years but are very difficult to quantitatively study because of the coexistence of the gravitationally-bound and outflow emission. We present detailed analysis of a heavily reddened quasar, SDSS J000610.67+121501.2, whose normal ultraviolet (UV) broad emission lines (BELs) are heavily suppressed by the Dusty Torus as a natural "Coronagraph", thus the blueshifted BELs (BBELs) can be reliably measured. The physical properties of the emission-line outflows are derived as follows: ionization parameter $U \sim 10^{-0.5}$, column density $N_{\rm H}\sim 10^{22.0}$ cm$^{-2}$, covering fraction of $\sim 0.1$ and upper limit density of $n_{\rm H}\sim 10^{5.8}$ cm$^{-3}$. The outflow gases are located at least 41 pc away from the central engine, which suggests that they have expanded to the scale of the dust torus or beyond. Besides, Lya shows a narrow symmetric component, to our surprise, which is undetected in any other lines. After inspecting the narrow emission-line region and the starforming region as the origin of the Lya narrow line, we propose the end-result of outflows, diffusing gases in the larger region, acts as the screen of Lya photons. Future high spatial resolution spectrometry and/or spectropolarimetric observation are needed to make a final clarification.
In hierarchical structure formation scenarios, merging galaxies are expected to be seen in different phases of their coalescence. Simulations suggest that simultaneous activity of the supermassive black holes (SMBHs) in the centres of the merging galaxies may be expected at kpc-scale separations. Currently, there are no direct observational methods which allow the selection of a large number of such dual active galactic nuclei (AGN) candidates. SDSS J142507.32+323137.4 was reported as a promising candidate source based on its optical spectrum. Here we report on our sensitive e-MERLIN observations performed at $1.6$ and at $5$ GHz, which show that the optical spectrum of the source can be more straightforwardly explained with jet-cloud interactions instead of the dual AGN scenario.
We present the catalog of the KVN Calibrator Survey (KVNCS). This first part of the KVNCS is a single dish radio survey conducted at 22 (K band) and 43 GHz (Q band) simultaneously using the Korean VLBI Network (KVN) from 2009 to 2011. A total 2045 sources selected from the VLBA Calibrator Survey (VCS) with an extrapolated flux density limit of 100 mJy at K band. The KVNCS contains 1533 sources in the K band with a flux density limit of 70 mJy and 553 sources in the Q band with a flux density limit of 120 mJy; it covers the whole sky down to $-32.^\circ5$ in declination. Five hundred thirteen sources were detected in the K and Q bands, simultaneously; $\sim76\%$ of them are flat-spectrum sources ($-0.5 \leq \alpha \leq 0.5$). From the flux--flux relationship, we anticipated that the most of the radiation of many of the sources comes from the compact components. Therefore, the sources listed in the KVNCS are strong candidates for high frequency VLBI calibrators.
The evolution of main sequence binaries resided in the galactic centre is influenced a lot by the central super massive black hole (SMBH). Due to this perturbation, the stars in a dense environment are likely to experience mergers or collisions through secular or non-secular interactions. In this work, we study the dynamics of the stellar binaries at galactic center, perturbed by another distant SMBH. Geometrically, such a four-body system is supposed to be decomposed into the inner triple (SMBH-star-star) and the outer triple (SMBH-stellar binary-SMBH). We survey the parameter space and determine the criteria analytically for the stellar mergers and the tidal disruption events (TDEs). For a relative distant and equal masses SMBH binary, the stars have more opportunities to merge as a result from the Lidov-Kozai(LK) oscillations in the inner triple. With a sample of tight stellar binaries, our numerical experiments reveal that a significant fraction of the binaries, ~70 per cent, experience merger eventually. Whereas the majority of the stellar TDEs are likely to occur at a close periapses to the SMBH, induced by the outer Kozai effect. The tidal disruptions are found numerically as many as ~10 per cent for a close SMBH binary that is enhanced significantly than the one without the external SMBH. These effects require the outer perturber to have an inclined orbit (>=40 degree) relatively to the inner orbital plane and may lead to a burst of the extremely astronomical events associated with the detection of the SMBH binary.
N-methylformamide, CH3NHCHO, may be an important molecule for interstellar pre-biotic chemistry because it contains a peptide bond. The rotational spectrum of the most stable trans conformer of CH3NHCHO is complicated by strong torsion-rotation interaction due to the low barrier of the methyl torsion. We use two absorption spectrometers in Kharkiv and Lille to measure the rotational spectra over 45--630 GHz. The analysis is carried out using the Rho-axis method and the RAM36 code. We search for N-methylformamide toward the hot molecular core Sgr B2(N2) using a spectral line survey carried out with ALMA. The astronomical results are put into a broader astrochemical context with the help of a gas-grain chemical kinetics model. The laboratory data set for the trans conformer of CH3NHCHO consists of 9469 line frequencies with J <= 62, including the first assignment of the rotational spectra of the first and second excited torsional states. All these lines are fitted within experimental accuracy. We report the tentative detection of CH3NHCHO towards Sgr B2(N2). We find CH3NHCHO to be more than one order of magnitude less abundant than NH2CHO, a factor of two less abundant than CH3NCO, but only slightly less abundant than CH3CONH2. The chemical models indicate that the efficient formation of HNCO via NH + CO on grains is a necessary step in the achievement of the observed gas-phase abundance of CH3NCO. Production of CH3NHCHO may plausibly occur on grains either through the direct addition of functional-group radicals or through the hydrogenation of CH3NCO. Provided the detection of CH3NHCHO is confirmed, the only slight underabundance of this molecule compared to its more stable structural isomer acetamide and the sensitivity of the model abundances to the chemical kinetics parameters suggest that the formation of these two molecules is controlled by kinetics rather than thermal equilibrium.
The Orion Nebula Cluster toward the HII region M42 is the most outstanding young cluster at the smallest distance 410pc among the rich high-mass stellar clusters. By newly analyzing the archival molecular data of the 12CO(J=1-0) emission at 21" resolution, we identified at least three pairs of complementary distributions between two velocity components at 8km/s and 13km/s. We present a hypothesis that the two clouds collided with each other and triggered formation of the high-mass stars, mainly toward two regions including the nearly ten O stars, theta1 Ori and theta2 Ori, in M42 and the B star, NU Ori, in M43. The timescale of the collision is estimated to be ~0.1Myr by a ratio of the cloud size and velocity corrected for projection, which is consistent with the age of the youngest cluster members less than 0.1Myr. The majority of the low-mass cluster members were formed prior to the collision in the last one Myr. We discuss implications of the present hypothesis and the scenario of high-mass star formation by comparing with the other eight cases of triggered O star formation via cloud-cloud collision.
The origin and life-cycle of molecular clouds are still poorly constrained, despite their importance for understanding the evolution of the interstellar medium. We have carried out a systematic, homogeneous, spectroscopic survey of the inner Galactic plane, in order to complement the many continuum Galactic surveys available with crucial distance and gas-kinematic information. Our aim is to combine this data set with recent infrared to sub-millimetre surveys at similar angular resolutions. The SEDIGISM survey covers 78 deg^2 of the inner Galaxy (-60 deg < l < +18 deg, |b| < 0.5 deg) in the J=2-1 rotational transition of 13CO. This isotopologue of CO is less abundant than 12CO by factors up to 100. Therefore, its emission has low to moderate optical depths, and higher critical density, making it an ideal tracer of the cold, dense interstellar medium. The data have been observed with the SHFI single-pixel instrument at APEX. The observational setup covers the 13CO(2-1) and C18O(2-1) lines, plus several transitions from other molecules. The observations have been completed. Data reduction is in progress, and the final data products will be made available in the near future. Here we give a detailed description of the survey and the dedicated data reduction pipeline. Preliminary results based on a science demonstration field covering -20 deg < l < -18.5 deg are presented. Analysis of the 13CO(2-1) data in this field reveals compact clumps, diffuse clouds, and filamentary structures at a range of heliocentric distances. By combining our data with data in the (1-0) transition of CO isotopologues from the ThrUMMS survey, we are able to compute a 3D realization of the excitation temperature and optical depth in the interstellar medium. Ultimately, this survey will provide a detailed, global view of the inner Galactic interstellar medium at an unprecedented angular resolution of ~30".
We study the significance of mergers in the quenching of star formation in galaxies at z~1 by examining their color-mass distributions for different morphology types. We perform two-dimensional light profile fits to GOODS iz images of ~5000 galaxies and X-ray selected active galactic nucleus (AGN) hosts in the CANDELS/GOODS-north and south fields in the redshift range 0.7<z<1.3. Distinguishing between bulge-dominated and disk-dominated morphologies, we find that disks and spheroids have distinct color-mass distributions, in agreement with studies at z~0. The smooth distribution across colors for the disk galaxies corresponds to a slow exhaustion of gas, with no fast quenching event. Meanwhile, blue spheroids most likely come from major mergers of star-forming disk galaxies, and the dearth of spheroids at intermediate green colors is suggestive of rapid quenching. The distribution of moderate luminosity X-ray AGN hosts is even across colors, in contrast, and we find similar numbers and distributions among the two morphology types with no apparent dependence on Eddington ratio. The high fraction of bulge-dominated galaxies that host an AGN in the blue cloud and green valley is consistent with the scenario in which the AGN is triggered after a major merger, and the host galaxy then quickly evolves into the green valley. This suggests AGN feedback may play a role in the quenching of star formation in the minority of galaxies that undergo major mergers.
Blazars are active galactic nuclei (AGN) whose relativistic jets point nearly to the line of sight. Their compact radio structure can be imaged with very long baseline interferometry (VLBI) on parsec scales. Blazars at extremely high redshifts provide a unique insight into the AGN phenomena in the early Universe. We observed four radio sources at redshift $z>4$ with the European VLBI Network (EVN) at 1.7 and 5 GHz. These objects were previously classified as blazar candidates based on X-ray observations. One of them, J2134$-$0419 is firmly confirmed as a blazar with our VLBI observations, due to its relativistically beamed radio emission. Its radio jet extended to $\sim$10 milli-arcsec scale makes this source a promising target for follow-up VLBI observations to reveal any apparent proper motion. Another target, J0839+5112 shows a compact radio structure typical of quasars. There is evidence for flux density variability and its radio "core" has a flat spectrum. However, the EVN data suggest that its emission is not Doppler-boosted. The remaining two blazar candidates (J1420+1205 and J2220+0025) show radio properties totally unexpected from radio AGN with small-inclination jet. Their emission extends to arcsec scales and the Doppler factors of the central components are well below 1. Their structures resemble that of double-lobed radio AGN with large inclination to the line of sight. This is in contrast with the blazar-type modeling of their multi-band spectral energy distributions. Our work underlines the importance of high-resolution VLBI imaging in confirming the blazar nature of high-redshift radio sources.
Most galactic nuclei harbor a massive black hole (MBH), whose birth and evolution are closely linked to those of its host galaxy. The unique conditions near the MBH: high velocity and density in the steep potential of a massive singular relativistic object, lead to unusual modes of stellar birth, evolution, dynamics and death. A complex network of dynamical mechanisms, operating on multiple timescales, deflect stars to orbits that intercept the MBH. Such close encounters lead to energetic interactions with observable signatures and consequences for the evolution of the MBH and its stellar environment. Galactic nuclei are astrophysical laboratories that test and challenge our understanding of MBH formation, strong gravity, stellar dynamics, and stellar physics. I review from a theoretical perspective the wide range of stellar phenomena that occur near MBHs, focusing on the role of stellar dynamics near an isolated MBH in a relaxed stellar cusp.
A new collection of photodissociation and photoionisation cross sections for
102 atoms and molecules of astrochemical interest has been assembled, along
with a brief review of the basic processes involved. These have been used to
calculate dissociation and ionisation rates, with uncertainties, in a standard
ultraviolet interstellar radiation field (ISRF) and wavelength-dependent
radiation fields. The new ISRF rates generally agree within 30% with our
previous compilations, with a few notable exceptions. The reduction of rates in
shielded regions was calculated as a function of dust, molecular and atomic
hydrogen, atomic C, and self-shielding column densities. The relative
importance of shielding types depends on the species in question and the dust
optical properties. The new data are publicly available from the Leiden
photodissociation and ionisation database.
Sensitivity of rates to variation of temperature and isotope, and cross
section uncertainties, are tested. Tests were conducted with an
interstellar-cloud chemical model, and find general agreement (within a factor
of two) with the previous iteration of the Leiden database for the ISRF, and
order-of-magnitude variations assuming various kinds of stellar radiation. The
newly parameterised dust-shielding factors makes a factor-of-two difference to
many atomic and molecular abundances relative to parameters currently in the
UDfA and KIDA astrochemical reaction databases. The newly-calculated cosmic-ray
induced photodissociation and ionisation rates differ from current standard
values up to a factor of 5. Under high temperature and cosmic-ray-flux
conditions the new rates alter the equilibrium abundances of abundant dark
cloud abundances by up to a factor of two. The partial cross sections for H2O
and NH3 photodissociation forming OH, O, NH2 and NH are also evaluated and lead
to radiation-field-dependent branching ratios.
[Abridged] We present spectroscopic observations in H$_{2}$O, CO and related species with \textit{Herschel} HIFI and PACS, as well as ground-based follow-up with the JCMT and APEX in CO, HCO$^{+}$ and isotopologues, of a sample of 49 nearby ($d<$500\,pc) candidate protostars. These data are used to study the outflow and envelope properties of these sources. We also compile their continuum SEDs in order to constrain their physical properties. Water emission is dominated by shocks associated with the outflow, rather than the cooler, slower entrained outflowing gas probed by ground-based CO observations. These shocks become less energetic as sources evolve from Class 0 to Class I. The fraction of mass in the outflow relative to the total envelope (i.e. $M_{\mathrm{out}}/M_{\mathrm{env}}$) remains broadly constant between Class 0 and I. The median value ($\sim$1$\%$) is consistent with a core to star formation efficiency on the order of 50$\%$ and an outflow duty cycle on the order of 5$\%$. Entrainment efficiency, as probed by $F_{\mathrm{CO}}/\dot{M}_{\mathrm{acc}}$, is also invariant with source properties and evolutionary stage. The median value (6.3\kms{}) suggests an entrainment efficiency of between 30 and 60$\%$ if the wind is launched at $\sim$1AU. $L$[O\,{\sc i}] is strongly correlated with $L_{\mathrm{bol}}$ but not with $M_{\mathrm{env}}$, while low-$J$ CO is more closely correlated with the latter than the former. This suggests that [O\,{\sc i}] traces the present-day accretion activity while CO traces time-averaged accretion over the dynamical timescale of the outflow. $L$[O\,{\sc i}] does not vary from Class 0 to Class I, unlike CO and H$_{2}$O. This is likely due to the ratio of atomic to molecular gas in the wind increasing as the source evolves, balancing out the decrease in mass accretion rate. Infall signatures are detected in HCO$^{+}$ and H$_{2}$O in a few sources.
The phase transition responsible for axion dark matter production can create large amplitude isocurvature perturbations which collapse into dense objects known as axion miniclusters. We use microlensing data from the EROS survey, and from recent observations with the Subaru Hyper Suprime Cam to place constraints on the minicluster scenario. We compute the microlensing event rate for miniclusters treating them as spatially extended objects with an extended mass function. Using the published bounds on the number of microlensing events we bound the fraction of DM collapsed into miniclusters, $f_{\rm MC}$. For an axion with temperature dependent mass consistent with the QCD axion we find $f_{\rm MC}<0.22(m_a/100\,\mu\text{eV})^{-0.57}$, which represents the first observational constraint on the minicluster fraction. We forecast that a high-efficiency observation of ten nights with Subaru would be sufficient to constrain $f_{\rm MC}\lesssim 0.1$ over the entire QCD axion mass range. We make various approximations to derive these constraints and dedicated analyses by the observing teams of EROS and Subaru are necessary to confirm our results. If accurate theoretical predictions for $f_{\rm MC}$ can be made in future then microlensing can be used to exclude, or discover, the QCD axion. Further details of our computations are presented in a companion paper.
We report on subarcsecond observations of complex organic molecules (COMs) in the high-mass protostar IRAS20126+4104 with the Plateau de Bure Interferometer in its most extended configurations. In addition to the simple molecules SO, HNCO and H2-13CO, we detect emission from CH3CN, CH3OH, HCOOH, HCOOCH3, CH3OCH3, CH3CH2CN, CH3COCH3, NH2CN, and (CH2OH)2. SO and HNCO present a X-shaped morphology consistent with tracing the outflow cavity walls. Most of the COMs have their peak emission at the putative position of the protostar, but also show an extension towards the south(east), coinciding with an H2 knot from the jet at about 800-1000 au from the protostar. This is especially clear in the case of H2-13CO and CH3OCH3. We fitted the spectra at representative positions for the disc and the outflow, and found that the abundances of most COMs are comparable at both positions, suggesting that COMs are enhanced in shocks as a result of the passage of the outflow. By coupling a parametric shock model to a large gas-grain chemical network including COMs, we find that the observed COMs should survive in the gas phase for about 2000 yr, comparable to the shock lifetime estimated from the water masers at the outflow position. Overall, our data indicate that COMs in IRAS20126+4104 may arise not only from the disc, but also from dense and hot regions associated with the outflow.
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We investigate the correlation of HCN 1-0 with dense gas mass in the Galactic center. We find that in general (on the ~10 pc size scale of individual molecular cloud cores) HCN 1-0 is well correlated with the dense molecular gas mass using a standard log-log relationship. However individual clouds in this environment show systematic deviations from this relationship that contribute to around 0.75 dex of scatter. Most notably, Sgr B2, the most massive cloud in the Galactic center, has an integrated HCN 1-0 intensity of cloud less than half its mass, and several other clouds including GCM-0.02-0.07 show an enhancement of HCN 1-0 by a factor of 2-3 relative to clouds of comparable mass. We also find that HCN 1-0 is more intense for a given mass in the large-scale diffuse emission in the central 300 parsecs compared to the compact emission from individual cloud cores. We identify the two primary sources of scatter in the relationship between HCN 1-0 and dense gas mass to be self-absorption (which reduces the observed HCN 1-0 intensity of Sgr B2) and variations in HCN abundance, which appear to increase the brightness of HCN 1-0 in GCM-0.02-0.07 and other clouds. We find that these sources of scatter would only contribute to an ~10% error in the dense gas mass inferred from the HCN 1-0 intensity in the Galactic center. However, the implied order of magnitude HCN abundance variations between Galactic center clouds, and the systematic nature of these variations warn of potential biases in the use of HCN as dense gas mass tracer in more extreme environments, such as AGN and shock-dominated regions. Finally, we also investigate other tracers having transitions near 3 mm, finding that HNCO, HNC and HCO+ largely behave like HCN, while HC3N, and CH3CN are higher fidelity tracers of the amount of gas in clouds like Sgr B2 that suffer from strong self-absorption of the HCN 1-0 line. [abridged]
We propose a simple analytic model to understand when star formation is time-steady versus bursty on short (<~10 Myr) time scales in galaxies. Recent models explain the observed Kennicutt-Schmidt relation between star formation rate and gas surface densities in galaxies as resulting from a balance between stellar feedback and gravity. We argue that bursty star formation occurs when such an equilibrium cannot be stably sustained, and identify two regimes in which galaxy-scale star formation should be bursty: i) at high redshift (z>~1) for galaxies of all masses, and ii) at low masses (depending on gas fraction) for galaxies at any redshift. At high redshift, characteristic galactic dynamical time scales become too short for supernova feedback to effectively respond to gravitational collapse in galactic discs (an effect recently identified for galactic nuclei), whereas in dwarf galaxies star formation occurs in too few bright star-forming regions to effectively average out. Burstiness is also enhanced at high redshift owing to elevated gas fractions in the early Universe. Our model can thus explain the bursty star formation histories observationally-inferred in both local dwarf and high-redshift galaxies, as well as the bursty star formation rates predicted in these regimes by recent high-resolution galaxy formation simulations. In our model, bursty star formation is associated with particularly strong spatio-temporal clustering of supernovae. Such clustering can promote the formation of galactic winds and our model may thus also explain the much higher wind mass loading factors inferred in high-redshift massive galaxies relative to their z~0 counterparts.
We present an analysis of archival ISO observations of pure-rotational lines of H2 in three pointings in the central 3 parsecs of the Galaxy: toward the Southwest region and Northeast region of the Galactic center Circumnuclear Disk, and toward the supermassive black hole Sgr A*. We detect pure rotational lines from 0-0 S(0) to S(13), as well as a number of rovibrationally excited transitions. From the pure rotational lines, we are able to describe the molecular gas with three discrete temperature components: a `hot' component between 500-600 K, a `hotter' component at 1250-1350 K, and a `hottest' component at > 2600 K. Toward Sgr A*, likely due to a combination of poorer baselines and weaker emission, we only detect a single hot component, at 1100 K. The observed excitation is consistent with heating via C-shocks. We also fit a continuous temperature distribution to the the S(1) through S(7) lines by assuming a power-law distribution of temperatures. We measure power law indices of n = 3.22 for the Northeast region and n = 2.83 for the Southwest region, with a smaller index indicating a higher fraction of warm gas. These indices are lower than those measured for other galaxies or other Galactic center clouds, which are measured to have n= 4-6. If we extrapolate this temperature distribution down to a cutoff temperature of 50 K, then the total molecular gas mass that we would measure for the Southwest (Northeast) region is 32 (140) % of the total molecular gas mass inferred from the dust emission, and 26 (125) % of the total molecular gas mass inferred from the CO emission for these regions. Ultimately, we find that the disagreement in the amount of mass recovered for these two regions means that this method cannot yet be verified to yield a reliable and independent estimate of the mass in the local region of the Circumnuclear Disk.
Magnetic fields are essential to fully understand the interstellar medium (ISM) and its role in the disk-halo interface of galaxies is still poorly understood. Star formation is known to expel hot gas vertically into the halo and these outflows have important consequences for mean-field dynamo theory in that they can be efficient in removing magnetic helicity. We perform new observations of the nearby face-on spiral galaxy NGC 628 with the Karl G. Jansky Very Large Array (JVLA) at S-band and the Effelsberg 100-m telescope at frequencies of 2.6 GHz and 8.35 GHz. We obtain some of the most sensitive radio continuum images in both total and linearly polarised intensity of any external galaxy observed so far in addition to high-quality images of Faraday depth and polarisation angle from which we obtained evidence for drivers of magnetic turbulence in the disk-halo connection. Such drivers include a superbubble detected via a significant Faraday depth gradient coinciding with a HI hole. We observe an azimuthal periodic pattern in Faraday depth with a pattern wavelength of 3.7$\pm$ 0.1 kpc, indicating Parker instabilities. The lack of a significant anti-correlation between Faraday depth and magnetic pitch angle indicates that these loops are vertical in nature with little helical twisting, unlike in IC 342. We find that the magnetic pitch angle is systematically larger than the morphological pitch angle of the polarisation arms which gives evidence for the action of a large-scale dynamo where the regular magnetic field is not coupled to the gas flow and obtains a significant radial component. We additionally discover a lone region of ordered magnetic field to the north of the galaxy with a high degree of polarisation and a small pitch angle, a feature that has not been observed in any other galaxy so far and is possibly caused by an asymmetric HI hole.
We present a new non-parametric Jeans code, GravSphere, that recovers the
density $\rho(r)$ and velocity anisotropy $\beta(r)$ of spherical stellar
systems, assuming only that they are in a steady-state. Using a large suite of
mock data, we confirm that with only line-of-sight velocity data, GravSphere
provides a good estimate of the density at the projected stellar half mass
radius, $\rho(R_{1/2})$, but is not able to measure $\rho(r)$ or $\beta(r)$,
even with 10,000 tracer stars. We then test three popular methods for breaking
this $\rho-\beta$ degeneracy: using multiple populations with different
$R_{1/2}$; using higher order `Virial Shape Parameters' (VSPs); and including
proper motion data.
We find that two populations provide an excellent recovery of $\rho(r)$
in-between their respective $R_{1/2}$. However, even with a total of $\sim
7,000$ tracers, we are not able to well-constrain $\beta(r)$ for either
population. By contrast, using 1000 tracers with higher order VSPs we are able
to measure $\rho(r)$ over the range $0.5 < r/R_{1/2} < 2$ and broadly constrain
$\beta(r)$. Including proper motion data for all stars gives an even better
performance, with $\rho$ and $\beta$ well-measured over the range $0.25 <
r/R_{1/2} < 4$.
Finally, we test GravSphere on a triaxial mock galaxy that has axis ratios
typical of a merger remnant, $[1:0.8:0.6]$. In this case, GravSphere can become
slightly biased. However, we find that when this occurs the data are poorly
fit, allowing us to detect when such departures from spherical symmetry become
problematic.
Here we present positions and radial velocities for over 4000 globular clusters (GCs) in 27 nearby early-type galaxies from the SLUGGS survey. The SLUGGS survey is designed to be representative of elliptical and lenticular galaxies in the stellar mass range 10 $<$ log M$_{\ast}$/M$_{\odot}$ $<$ 11.7. The data have been obtained over many years, mostly using the very stable multi-object spectrograph DEIMOS on the Keck II 10m telescope. Radial velocities are measured using the calcium triplet lines with a velocity accuracy of $\pm$ 10-15 km/s. We use phase space diagrams (i.e. velocity--position diagrams) to identify contaminants such as foreground stars and background galaxies, and to show that the contribution of GCs from neighboring galaxies is generally insignificant. Likely ultra-compact dwarfs are tabulated separately. We find that the mean velocity of the GC system is close to that of the host galaxy systemic velocity, indicating that the GC system is in overall dynamical equilibrium within the galaxy potential. We also find that the GC system velocity dispersion scales with host galaxy stellar mass in a similar manner to the Faber-Jackson relation for the stellar velocity dispersion. Publication of these GC radial velocity catalogs should enable further studies in many areas, such as GC system substructure, kinematics, and host galaxy mass measurements.
The total mass M_GCS in the globular cluster (GC) system of a galaxy is empirically a near-constant fraction of the total mass M_h = M_bary + M_dark of the galaxy, across a range of 10^5 in galaxy mass. This trend is radically unlike the strongly nonlinear behavior of total stellar mass M_star versus M_h. We discuss extensions of this trend to two more extreme situations: (a) entire clusters of galaxies, and (b) the Ultra-Diffuse Galaxies (UDGs) recently discovered in Coma and elsewhere. Our calibration of the ratio \eta_M = M_GCS / M_h from normal galaxies, accounting for new revisions in the adopted mass-to-light ratio for GCs, now gives \eta_M = 2.9 \times 10^{-5} as the mean absolute mass fraction. We find that the same ratio appears valid for galaxy clusters and UDGs. Estimates of \eta_M in the four clusters we examine tend to be slightly higher than for individual galaxies, butmore data and better constraints on the mean GC mass in such systems are needed to determine if this difference is significant. We use the constancy of \eta_M to estimate total masses for several individual cases; for example, the total mass of the Milky Way is calculated to be M_h = 1.1 \times 10^{12} M_sun. Physical explanations for the uniformity of \eta_M are still descriptive, but point to a picture in which massive, dense star clusters in their formation stages were relatively immune to the feedback that more strongly influenced lower-density regions where most stars form.
Measurements of element abundances in galaxies from astrophysical
spectroscopy depend sensitively on the atomic data used. With the goal of
making the latest atomic data accessible to the community, we present a
compilation of selected atomic data for resonant absorption lines at
wavelengths longward of 911.753 {\AA} (the \ion{H}{1} Lyman limit), for key
heavy elements (heavier than atomic number 5) of astrophysical interest. In
particular, we focus on the transitions of those ions that have been observed
in the Milky Way interstellar medium (ISM), the circumgalactic medium (CGM) of
the Milky Way and/or other galaxies, and the intergalactic medium (IGM).
We provide wavelengths, oscillator strengths (both previous and new
determinations, where available), associated accuracy grades, and references to
the oscillator strength determinations. We also attempt to compare and assess
the recent oscillator strength determinations. For about 22\% of the lines that
have updated oscillator strength values, the differences between the former
values and the updated ones are $\gtrsim$~0.1 dex.
Our compilation will be a useful resource for absorption line studies of the
ISM, as well as studies of the CGM and IGM traced by sight lines to quasars and
gamma-ray bursts. Studies (including those enabled by future generations of
extremely large telescopes) of absorption by galaxies against the light of
background galaxies will also benefit from our compilation.
We present the discovery and spectroscopic confirmation with the ESO NTT and Gemini South telescopes of eight new 6.0 < z < 6.5 quasars with z$_{AB}$ < 21.0. These quasars were photometrically selected without any star-galaxy morphological criteria from 1533 deg$^{2}$ using SED model fitting to photometric data from the Dark Energy Survey (g, r, i, z, Y), the VISTA Hemisphere Survey (J, H, K) and the Wide-Field Infrared Survey Explorer (W1, W2). The photometric data was fitted with a grid of quasar model SEDs with redshift dependent Lyman-{\alpha} forest absorption and a range of intrinsic reddening as well as a series of low mass cool star models. Candidates were ranked using on a SED-model based $\chi^{2}$-statistic, which is extendable to other future imaging surveys (e.g. LSST, Euclid). Our spectral confirmation success rate is 100% without the need for follow-up photometric observations as used in other studies of this type. Combined with automatic removal of the main types of non-astrophysical contaminants the method allows large data sets to be processed without human intervention and without being over run by spurious false candidates. We also present a robust parametric redshift estimating technique that gives comparable accuracy to MgII and CO based redshift estimators. We find two z $\sim$ 6.2 quasars with HII near zone sizes < 3 proper Mpc which could indicate that these quasars may be young with ages < 10$^6$ - 10$^7$ years or lie in over dense regions of the IGM. The z = 6.5 quasar VDESJ0224-4711 has J$_{AB}$ = 19.75 is the second most luminous quasar known with z > 6.5.
We present 450 and 850 micron submillimetre continuum observations of the IC5146 star-forming region taken as part of the JCMT Gould Belt Survey. We investigate the location of bright submillimetre (clumped) emission with the larger-scale molecular cloud through comparison with extinction maps, and find that these denser structures correlate with higher cloud column density. Ninety-six individual submillimetre clumps are identified using FellWalker and their physical properties are examined. These clumps are found to be relatively massive, ranging from 0.5to 116 MSun with a mean mass of 8 MSun and a median mass of 3.7 MSun. A stability analysis for the clumps suggest that the majority are (thermally) Jeans stable, with M/M_J < 1. We further compare the locations of known protostars with the observed submillimetre emission, finding that younger protostars, i.e., Class 0 and I sources, are strongly correlated with submillimetre peaks and that the clumps with protostars are among the most Jeans unstable. Finally, we contrast the evolutionary conditions in the two major star-forming regions within IC5146: the young cluster associated with the Cocoon Nebula and the more distributed star formation associated with the Northern Streamer filaments. The Cocoon Nebula appears to have converted a higher fraction of its mass into dense clumps and protostars, the clumps are more likely to be Jeans unstable, and a larger fraction of these remaining clumps contain embedded protostars. The Northern Streamer, however, has a larger number of clumps in total and a larger fraction of the known protostars are still embedded within these clumps.
The velocity distribution of dark matter near the Earth is important for an accurate analysis of the signals in terrestrial detectors. This distribution is typically extracted from numerical simulations. Here we address the possibility of deriving the velocity distribution function analytically. We derive a differential equation which is a function of radius and the radial component of the velocity. Under various assumptions this can be solved, and we compare the solution with the results from controlled numerical simulations. Our findings complement the previously derived tangential velocity distribution. We hereby demonstrate that the entire distribution function, below 0.7 v_esc, can be derived analytically for spherical and equilibrated dark matter structures.
The CO-to-H$_2$ conversion factor ($X_\mathrm{CO}$) is known to correlate with the metallicity ($Z$). The dust abundance, which is related to the metallicity, is responsible for this correlation through dust shielding of dissociating photons and H$_2$ formation on dust surfaces. In this paper, we investigate how the relation between dust-to-gas ratio and metallicity ($\mathcal{D}$--$Z$ relation) affects the H$_2$ and CO abundances (and $X_\mathrm{CO}$) of a `molecular' cloud. For the $\mathcal{D}$--$Z$ relation, we adopt a dust evolution model developed in our previous work, which treats the evolution of not only dust abundance but also grain sizes in a galaxy. Shielding of dissociating photons and H$_2$ formation on dust are solved consistently with the dust abundance and grain sizes. As a consequence, our models {predict consistent metallicity dependence of $X_\mathrm{CO}$ with observational data}. Among various processes driving dust evolution, grain growth by accretion has the largest impact on the $X_\mathrm{CO}$--$Z$ relation. The other processes also have some impacts on the $X_\mathrm{CO}$--$Z$ relation, but their effects are minor compared with the scatter of the observational data at the metallicity range ($Z\gtrsim 0.1$ Z$_\odot$) where CO could be detected. We also find that dust condensation in stellar ejecta has a dramatic impact on the H$_2$ abundance at low metallicities ($\lesssim 0.1$ Z$_\odot$), relevant for damped Lyman $\alpha$ systems and nearby dwarf galaxies, and that the grain size dependence of H$_2$ formation rate is also important.
We derive a new relation between the metallicity of Seyfert 2 Active Galactic Nuclei (AGNs) and the intensity of the narrow emission-lines ratio $N2O2$=log([N II]$\lambda$6584/[O II]$\lambda$3727). The calibration of this relation was performed determining the metallicity ($Z$) of a sample of 58 AGNs through a diagram containing the observational data and the results of a grid of photoionization models obtained with the Cloudy code. We find the new $Z/Z_\odot$-$N2O2$ relation using the obtained metallicity values and the corresponding observational emission line intensities for each object of the sample. Estimations derived through the use of this new calibration indicate that narrow line regions of Seyfert 2 galaxies exhibit a large range of metallicities ($0.3 \: < \: Z/Z_{\odot} \: < \:2.0$), with a median value $Z \approx Z_{\odot}$. Regarding the possible existence of correlations between the luminosity $L(\rm H\beta$), the electron density, and the color excess E(B$-$V) with the metallicity in this kind of objects, we do not find correlations between them.
We present a detailed study of a molecular outflow feature in the nearby starburst galaxy NGC 253 using ALMA. We find that this feature is clearly associated with the edge of NGC 253's prominent ionized outflow, has a projected length of ~300 pc, with a width of ~50 pc and a velocity dispersion of ~40 km s^-1, consistent with an ejection from the disk about 1 Myr ago. The kinematics of the molecular gas in this feature can be interpreted (albeit not uniquely) as accelerating at a rate of 1 km s^-1 pc^-1. In this scenario, the gas is approaching escape velocity at the last measured point. Strikingly, bright tracers of dense molecular gas (HCN, CN, HCO+, CS) are also detected in the molecular outflow: We measure an HCN(1-0)/CO(1-0) line ratio of ~1/10 in the outflow, similar to that in the central starburst region of NGC 253 and other starburst galaxies. By contrast, the HCN/CO line ratio in the NGC 253 disk is significantly lower (~1/30), similar to other nearby galaxy disks. This strongly suggests that the streamer gas originates from the starburst, and that its physical state does not change significantly over timescales of ~1 Myr during its entrainment in the outflow. Simple calculations indicate that radiation pressure is not the main mechanism for driving the outflow. The presence of such dense material in molecular outflows needs to be accounted for in simulations of galactic outflows.
It has been well established in the past decades that the central black hole masses of galaxies correlate with dynamical properties of their harbouring bulges. This notion begs the question of whether there are causal connections between the AGN and its immediate vicinity in the host galaxy. In this paper we analyse the presence of circumnuclear star formation in a sample of 15 AGN using mid-infrared observations. The data consist of a set of 11.3{\mm} PAH emission and reference continuum images, taken with ground based telescopes, with sub-arcsecond resolution. By comparing our star formation estimates with AGN accretion rates, derived from X-ray luminosities, we investigate the validity of theoretical predictions for the AGN-starburst connection. Our main results are: i) circumnuclear star formation is found, at distances as low as tens of parsecs from the nucleus, in nearly half of our sample (7/15); ii) star formation luminosities are correlated with the bolometric luminosity of the AGN ($L_{AGN}$) only for objects with $L_{AGN} \ge 10^{42}\,\,{\rm erg\,\,s^{-1}}$; iii) low luminosity AGNs ($L_{AGN} < 10^{42}\,\,{\rm erg\,\,s^{-1}}$) seem to have starburst luminosities far greater than their bolometric luminosities.
The distance to the planetary system OGLE-2015-BLG-0966L and the separation between the planet and its host star are ambiguous due to an ambiguity in the distance to the source star (Street et al. 2016). We attempt to break this degeneracy by measuring the systemic radial velocity of the source star measured from a spectrum taken while the source was highly magnified. Our measurement of v_{LSR} = 53 +/- 1 km s^{-1} does not definitively resolve the nature of the source, but supports the general conclusion that the source is in the bulge. Although in this case the measured radial velocity was inconclusive, this work demonstrates that even a low signal-to-noise spectrum can provide useful information for characterizing microlensing source stars.
Mergers of galaxies are thought to cause significant gas inflows to the inner parsecs, which can activate rapid accretion onto supermassive black holes (SMBHs), giving rise to Active Galactic Nuclei (AGN). During a significant fraction of this process, SMBHs are predicted to be enshrouded by gas and dust. Studying 52 galactic nuclei in infrared-selected local Luminous and Ultra-luminous infrared galaxies in different merger stages in the hard X-ray band, where radiation is less affected by absorption, we find that the amount of material around SMBHs increases during the last phases of the merger. We find that the fraction of Compton-thick (CT, $N_{\rm\,H}\geq 10^{24}\rm\,cm^{-2}$) AGN in late merger galaxies is higher ($f_{\rm\,CT}=65^{+12}_{-13}\%$) than in local hard X-ray selected AGN ($f_{\rm\,CT}=27\pm 4\%$), and that obscuration reaches its maximum when the nuclei of the two merging galaxies are at a projected distance of $D_{12}\simeq0.4-10.8$ kiloparsecs ($f_{\rm\,CT}=77_{-17}^{+13}\%$). We also find that all AGN of our sample in late merger galaxies have $N_{\rm\,H}> 10^{23}\rm\,cm^{-2}$, which implies that the obscuring material covers $95^{+4}_{-8}\%$ of the X-ray source. These observations show that the material is most effectively funnelled from the galactic scale to the inner tens of parsecs during the late stages of galaxy mergers, and that the close environment of SMBHs in advanced mergers is richer in gas and dust with respect to that of SMBHs in isolated galaxies, and cannot be explained by the classical AGN unification model in which the torus is responsible for the obscuration.
With a high value of heliocentric radial velocity, a retrograde orbit, and being suspected to have an extragalactic origin, NGC 3201 is an interesting globular cluster for kinematical studies. Our purpose is to calculate the relative proper motions (PMs) and membership probability for the stars in the wide region of globular cluster NGC 3201. Proper motion based membership probabilities are used to isolate the cluster sample from the field stars. The membership catalogue will help address the question of chemical inhomogeneity in the cluster. Archive CCD data taken with a wide-field imager (WFI) mounted on the ESO 2.2m telescope are reduced using the high-precision astrometric software developed by Anderson et al. for the WFI images. The epoch gap between the two observational runs is $\sim$14.3 years. To standardize the $BVI$ photometry, Stetson's secondary standard stars are used. The CCD data with an epoch gap of $\sim$14.3 years enables us to decontaminate the cluster stars from field stars efficiently. The median precision of PMs is better than $\sim$0.8 mas~yr$^{-1}$ for stars having $V<$18 mag that increases up to $\sim$1.5 mas~yr$^{-1}$ for stars with $18<V<20$ mag. Kinematic membership probabilities are calculated using proper motions for stars brighter than $V\sim$20 mag. An electronic catalogue of positions, relative PMs, $BVI$ magnitudes and membership probabilities in $\sim$19.7$\times$17 arcmin$^2$ region of NGC 3201 is presented. We use our membership catalogue to identify probable cluster members among the known variables and $X$-ray sources in the direction of NGC 3201.
FUors are young stellar objects experiencing large optical outbursts due to highly enhanced accretion from the circumstellar disk onto the star. FUors are often surrounded by massive envelopes, which play a significant role in the outburst mechanism. Conversely, the subsequent eruptions might gradually clear up the obscuring envelope material and drive the protostar on its way to become a disk-only T Tauri star. Here we present an APEX $^{12}$CO and $^{13}$CO survey of eight southern and equatorial FUors. We measure the mass of the gaseous material surrounding our targets. We locate the source of the CO emission and derive physical parameters for the envelopes and outflows, where detected. Our results support the evolutionary scenario where FUors represent a transition phase from envelope-surrounded protostars to classical T Tauri stars.
Optical and near-infrared photometry, optical spectroscopy, and soft X-ray and UV monitoring of the changing look active galactic nucleus NGC 2617 show that it continues to have the appearance of a type-1 Seyfert galaxy. An optical light curve for 2010--2016 indicates that the change of type probably occurred between October 2010 and February 2012 and was not related to the brightening in 2013. In 2016 NGC 2617 brightened again to a level of activity close to that of April 2013. We find variations in all passbands and in both the intensities and profiles of the broad Balmer lines. A new displaced emission peak has appeared in H$\beta$. X-ray variations are well correlated with UV--optical variability and possibly lead by $\sim$ 2--3 days. The $K$ band lags the $J$ band by about 21.5 $\pm$ 2.5 days and lags the combined $B+J$ filters by $\sim$ 25 days. $J$ lags $B$ by about 3 days. This could be because $J$-band variability arises from the outer part of the accretion disc while $K$-band variability comes from thermal re-emission by dust. We propose that spectral type changes are a result of increasing central luminosity causing sublimation of the innermost dust in the hollow bi-conical outflow. We briefly discuss various other possible reasons which might explain the dramatic changes NGC 2617.
We report on the measurement of the trigonometric parallaxes of 1612 MHz hydroxyl masers around two asymptotic giant branch stars, WX Psc and OH138.0+7.2, using the NRAO Very Long Baseline Array with in-beam phase referencing calibration. We obtained a 3-sigma upper limit of <=5.3 mas on the parallax of WX Psc, corresponding to a lower limit distance estimate of >~190 pc. The obtained parallax of OH138.0+7.2 is 0.52+/-0.09 mas (+/-18%), corresponding to a distance of 1.9(+0.4,-0.3) kpc, making this the first hydroxyl maser parallax below one milliarcsecond. We also introduce a new method of error analysis for detecting systematic errors in the astrometry. Finally, we compare our trigonometric distances to published phase-lag distances toward these stars and find a good agreement between the two methods.
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We introduce a new model for the formation and evolution of supermassive
black holes (SMBHs) in the RAMSES code using sink particles, improving over
previous work the treatment of gas accretion and dynamical evolution. This new
model is tested against a suite of high-resolution simulations of an isolated,
gas-rich, cooling halo. We study the effect of various feedback models on the
SMBH growth and its dynamics within the galaxy.
In runs without any feedback, the SMBH is trapped within a massive bulge and
is therefore able to grow quickly, but only if the seed mass is chosen larger
than the minimum Jeans mass resolved by the simulation. We demonstrate that, in
the absence of supernovae (SN) feedback, the maximum SMBH mass is reached when
Active Galactic Nucleus (AGN) heating balances gas cooling in the nuclear
region.
When our efficient SN feedback is included, it completely prevents bulge
formation, so that massive gas clumps can perturb the SMBH orbit, and reduce
the accretion rate significantly. To overcome this issue, we propose an
observationally motivated model for the joint evolution of the SMBH and a
parent nuclear star cluster (NSC), which allows the SMBH to remain in the
nuclear region, grow fast and resist external perturbations. In this scenario,
however, SN feedback controls the gas supply and the maximum SMBH mass now
depends on the balance between AGN heating and gravity. We conclude that
SMBH/NSC co-evolution is crucial for the growth of SMBH in high-z galaxies, the
progenitors of massive elliptical today.
We confirm two new local massive relic galaxies, i.e. untouched survivors of the early universe massive population: Mrk1216 and PGC032873. Both show early and peaked formation events within very short timescales (<1 Gyr) and thus old mean mass-weighted ages (~13 Gyr). Their star formation histories remain virtually unchanged out to several effective radii, even when considering the steeper IMF values inferred out to ~3 effective radii. Their morphologies, kinematics and density profiles are like those found in the z>2 massive population, setting them apart of the typical z~0 massive early-type galaxies. We find that there seems to exist a "degree of relic" that is related on how far into the path to become one of these typical z~0 massive galaxies the compact relic has undergone. This path is partly dictated by the environment the galaxy lives in. For galaxies in rich environments, such as the previously reported relic galaxy NGC1277, the most extreme properties (e.g. sizes, short formation timescales, larger super-massive black holes) are expected, while lower density environments will have galaxies with delayed and/or extended star formations, slightly larger sizes and not that extreme black hole masses. The confirmation of 3 relic galaxies up to a distance of 106Mpc implies a lower limit in the number density of these red nuggets in the local universe of 6x10^{-7} Mpc^{3}, which is within the theoretical expectations.
Several recent studies have reported different intrinsic correlations between the AGN mid-IR luminosity ($L_{MIR}$) and the rest-frame 2-10 keV luminosity ($L_{X}$) for luminous quasars. To understand the origin of the difference in the observed $L_{X}-L_{MIR}$ relations, we study a sample of 3,247 spectroscopically confirmed type 1 AGNs collected from Bo\"{o}tes, XMM-COSMOS, XMM-XXL-North, and the SDSS quasars in the Swift/XRT footprint spanning over four orders of magnitude in luminosity. We carefully examine how different observational constraints impact the observed $L_{X}-L_{MIR}$ relations, including the inclusion of X-ray non-detected objects, possible X-ray absorption in type 1 AGNs, X-ray flux limits, and star formation contamination. We find that the primary factor driving the different $L_{X}-L_{MIR}$ relations reported in the literature is the X-ray flux limits for different studies. When taking these effects into account, we find that the X-ray luminosity and mid-IR luminosity (measured at rest-frame $6\mu m$, or $L_{6\mu m}$) of our sample of type 1 AGNs follow a bilinear relation in the log-log plane: $\log L_X =(0.84\pm0.03)\times\log L_{6\mu m}/10^{45}{\rm erg\;s^{-1}} + (44.60\pm0.01)$ for $L_{6\mu m} < 10^{44.79}{\rm erg\;s^{-1}} $, and $\log L_X = (0.40\pm0.03)\times\log L_{6\mu m}/10^{45}{\rm erg\;s^{-1}} +(44.51\pm0.01)$ for $L_{6\mu m} \geq 10^{44.79}{\rm erg\;s^{-1}} $. This suggests that the luminous type 1 quasars have a shallower $L_{X}-L_{MIR}$ correlation than the approximately linear relations found in local Seyfert galaxies. This result is consistent with previous studies reporting a luminosity-dependent $L_{X}-L_{MIR}$ relation, and implies that assuming a linear $L_{X}-L_{MIR}$ relation to infer the neutral gas column density for X-ray absorption might overestimate the column densities in luminous quasars.
We consider the evolution of an outburst in a uniform medium under spherical symmetry, having in mind AGN feedback in the intra cluster medium (ICM). For a given density and pressure of the medium, the spatial structure and energy partition at a given time $t_{age}$ (since the onset of the outburst) are fully determined by the total injected energy $E_{inj}$ and the duration $t_b$ of the outburst. We are particularly interested in the late phase evolution when the strong shock transforms into a sound wave. We studied the energy partition during such transition with different combinations of $E_{inj}$ and $t_b$. For an instantaneous outburst with $t_b\rightarrow 0$, which corresponds to the extension of classic Sedov-Taylor solution with counter-pressure, the fraction of energy that can be carried away by sound waves is $\lesssim$12% of $E_{inj}$. As $t_b$ increases, the solution approaches the "slow piston" limit, with the fraction of energy in sound waves approaching zero. We then repeat the simulations using radial density and temperature profiles measured in Perseus and M87/Virgo clusters. We find that the results with a uniform medium broadly reproduce an outburst in more realistic conditions once proper scaling is applied. We also develop techniques to map intrinsic properties of an outburst $(E_{inj}, t_b$ and $t_{age})$ to the observables like the Mach number of the shock and radii of the shock and ejecta. For the Perseus cluster and M87, the estimated $(E_{inj}, t_b$ and $t_{age})$ agree with numerical simulations tailored for these objects with $20-30\%$ accuracy.
NGC 1313 is a bulgeless nearby galaxy, classified as SB(s)d. Its proximity allows high spatial resolution observations. We performed the first detailed analysis of the emission-line properties in the nuclear region of NGC 1313, using an optical data cube obtained with the Gemini Multi-object Spectrograph. We detected four main emitting areas, three of them (regions 1, 2 and 3) having spectra typical of H II regions. Region 1 is located very close to the stellar nucleus and shows broad spectral features characteristic of Wolf-Rayet stars. Our analysis revealed the presence of one or two WC4-5 stars in this region, which is compatible with results obtained by previous studies. Region 4 shows spectral features (as a strong H$\alpha$ emission line, with a broad component) typical of a massive emission-line star, such as a luminous blue variable, a B[e] supergiant or a B hypergiant. The radial velocity map of the ionized gas shows a pattern consistent with rotation. A significant drop in the values of the gas velocity dispersion was detected very close to region 1, which suggests that the young stars there were formed from this cold gas, possibly keeping low values of velocity dispersion. Therefore, although detailed measurements of the stellar kinematics were not possible (due to the weak stellar absorption spectrum of this galaxy), we predict that NGC 1313 may also show a drop in the values of the stellar velocity dispersion in its nuclear region.
It has yet to be established whether the properties of the gas in distant protocluster galaxies are significantly affected by their environment as they are in galaxies in local clusters. Through a deep, 64 hours of effective on-source integration with the ATCA, we discovered a very massive, M_mol=2.0+-0.2x10^11 M_sun, very extended, ~40 kpc, CO(1-0)-emitting disk in the protocluster surrounding the radio galaxy, MRC1138-262. The galaxy, at a redshift z_CO=2.1478, is a clumpy massive disk galaxy, M_star~5x10^11 M_sun, which lies 300 kpc in projection from MRC1138-262 and is a known H-alpha emitter, HAE229. The bulk of the CO emission shows a kinematic gradient along the major axis of the disk, consistent with rotation. A significant fraction of the CO emission lies outside of the UV/optical emitting galaxy and the galaxy has a molecular gas fraction, f_mol~30%. HAE229 follows the relation of normal field star-forming galaxies between star-formation rate and molecular gas mass. HAE229 is the first CO(1-0) detection of an ordinary, star-forming galaxy in a high-redshift protocluster and only the third robust CO(1-0) detection of an H-alpha emitting galaxy in an high-z overdensity. We compare a sample of cluster members at z>0.4 that are detected in low-order CO transitions with a similar sample of sources drawn from the field. We confirm recent findings that the CO-luminosity and FWHM are correlated in dusty starbursts and show that this relation is valid for normal high-z galaxies as well as those in overdensities. We do not find a clear dichotomy in the integrated Schmidt-Kennicutt relation for protocluster and field galaxies. Not finding any environmental dependence in the molecular gas content or star-formation efficiency of galaxies, suggests that environmentally-specific processes such as ram pressure stripping are not operating efficiently in high-z (proto)clusters. (abridged)
I demonstrate four tight correlations of total baryonic mass, velocity and radius for a set of nearby disk galaxies: the Mass-Velocity relation $ Mt \propto V^4$; the Mass-Radius relation $ Mt \propto R^2$; the Radius-Velocity relation $R \propto V^2$; and the Mass-Radius-Velocity relation $ Mt \propto R V^2$. The Mass-Velocity relation is the familiar Baryonic Tully-Fisher relation(BTFR) and versions of the other three relations, using magnitude rather than baryonic mass, are also well known. These four observed correlations follow from a pair of more fundamental relations. First, the centripetal acceleration at the edge of the stellar disk is proportional to the acceleration predicted by Newtonian physics and secondly, this acceleration is a constant which is related to Milgrom's constant. The two primary relations can be manipulated algebraically to generate the four observed correlations and allow little room for dark matter inside the radius of the stellar disk. The primary relations do not explain the velocity of the outer gaseous disks of spiral galaxies which do not trace the Newtonian gravitational field of the observed matter.
We report the $4 \, \sigma$ detection of a faint object with a flux of ~ 0.3 mJy, in the vicinity of the quadruply lensed QSO MG0414+0534 using the Atacama Large Millimeter/submillimeter array (ALMA) Band 7. The object is most probably a dusty dark dwarf galaxy, which has not been detected in either the optical, near-infrared (NIR) or radio (cm) bands. An anomaly in the flux ratio of the lensed images observed in Band 7 and the mid-infrared (MIR) band and the reddening of the QSO light color can be simultaneously explained if we consider the object as a lensing substructure with an ellipticity ~ 0.7 at a redshift of $0.5 \lesssim z \lesssim 1$. Using the best-fit lens models with three lenses, we find that the dark matter plus baryon mass associated with the object is $\sim 10^9\, M_{\odot}$, the dust mass is $\sim 10^7\,M_{\odot}$ and the linear size is $\gtrsim 5\,$kpc. Thus our findings suggest that the object is a dusty dark dwarf galaxy. A substantial portion of faint submillimeter galaxies (SMGs) in the universe may be attributed to such dark objects.
Isolated HI clouds with no optical counterparts are often taken as evidence for galaxy-galaxy interactions, though an alternative hypothesis is that these are primordial 'dark galaxies' which have not formed stars. Similarly, certain kinematic features in HI streams are also controversial, sometimes taken as evidence of dark galaxies but also perhaps explicable as the result of harassment. We numerically model the passage of a galaxy through the gravitational field of cluster. The galaxy consists of SPH particles for the gas and n-bodies for the stars and dark matter, while the cluster includes the gravitational effects of substructure using 400 subhalos (the effects of the intracluster medium are ignored). We find that harassment can indeed produce long HI streams and these streams can include kinematic features resembling dark galaxy candidates such as VIRGOHI21. We also show that apparent clouds with diameter < 20 kpc and velocity widths < 50 km/s are almost invariably produced in these simulations, making tidal debris a highly probable explanation. In contrast, we show that the frequency of isolated clouds of the same size but velocity width > 100 km/s is negligible - making this a very unlikely explanation for the observed clouds in the Virgo cluster with these properties.
We present the second release of value-added catalogues of the LAMOST Spectroscopic Survey of the Galactic Anticentre (LSS-GAC DR2). The catalogues present values of radial velocity $V_{\rm r}$, atmospheric parameters --- effective temperature $T_{\rm eff}$, surface gravity log$g$, metallicity [Fe/H], $\alpha$-element to iron (metal) abundance ratio [$\alpha$/Fe] ([$\alpha$/M]), elemental abundances [C/H] and [N/H], and absolute magnitudes ${\rm M}_V$ and ${\rm M}_{K_{\rm s}}$ deduced from 1.8 million spectra of 1.4 million unique stars targeted by the LSS-GAC since September 2011 until June 2014. The catalogues also give values of interstellar reddening, distance and orbital parameters determined with a variety of techniques, as well as proper motions and multi-band photometry from the far-UV to the mid-IR collected from the literature and various surveys. Accuracies of radial velocities reach 5kms$^{-1}$ for late-type stars, and those of distance estimates range between 10 -- 30 per cent, depending on the spectral signal-to-noise ratios. Precisions of [Fe/H], [C/H] and [N/H] estimates reach 0.1dex, and those of [$\alpha$/Fe] and [$\alpha$/M] reach 0.05dex. The large number of stars, the contiguous sky coverage, the simple yet non-trivial target selection function and the robust estimates of stellar radial velocities and atmospheric parameters, distances and elemental abundances, make the catalogues a valuable data set to study the structure and evolution of the Galaxy, especially the solar-neighbourhood and the outer disk.
Extremely metal-poor, high-ionizing starbursts in the local Universe provide unique laboratories for exploring in detail the physics of high-redshift systems. Also, their ongoing star-formation and haphazard morphology make them outstanding proxies for primordial galaxies. Using integral field spectroscopy, we spatially resolved the ISM properties and massive stars of two first-class low metallicity galaxies with Wolf-Rayet features and nebular HeII emission: Mrk178 and IZw18. In this review, we summarize our main results for these two objects.
Strong gravitational lensing provides a powerful test of Cold Dark Matter (CDM) as it enables the detection and mass measurement of low mass haloes even if they do not contain baryons. Compact lensed sources such as Active Galactic Nuclei (AGN) are particularly sensitive to perturbing subhalos, but their use as a test of CDM has been limited by the small number of systems which have significant radio emission. Radio emission is extended enough avoid significant lensing by stars in the plane of the lens galaxy, and red enough to be minimally affected by differential dust extinction. Narrow-line emission is a promising alternative as it is also extended and, unlike radio, detectable in virtually all optically selected AGN lenses. We present first results from a WFC3 grism narrow-line survey of lensed quasars, for the quadruply lensed AGN HE0435-1223. Using a forward modelling pipeline which enables us to robustly account for blending between nearby images and the main lens galaxy, we measure the [OIII] 5007 \AA$~$ flux ratios of the four lensed quasar images. We find that the lensed [OIII] fluxes and positions are well fit by a simple smooth mass model for the main lens. Our data rule out a $>10^{8} (10^{7.2}) M_{600}/M_\odot$ NFW perturber within $\sim$1."0 (0."1) arcseconds of the lensed images, where $M_{600}$ is the perturber mass within its central 600 pc. The non-detection is broadly consistent with the expectations of $\Lambda$CDM for a single system. The sensitivity achieved demonstrates that powerful limits on the nature of dark matter can be obtained with the analysis of the entire sample of narrow-line lenses.
We report ALMA Cycle 2 observations of 230 GHz (1.3 mm) dust continuum emission, and $^{12}$CO, $^{13}$CO, and C$^{18}$O J = 2-1 line emission, from the Upper Scorpius transitional disk [PZ99] J160421.7-213028, with an angular resolution of ~0".25 (35 AU). Armed with these data and existing H-band scattered light observations, we measure the size and depth of the disk's central cavity, and the sharpness of its outer edge, in three components: sub-$\mu$m-sized "small" dust traced by scattered light, millimeter-sized "big" dust traced by the millimeter continuum, and gas traced by line emission. Both dust populations feature a cavity of radius $\sim$70 AU that is depleted by factors of at least 1000 relative to the dust density just outside. The millimeter continuum data are well explained by a cavity with a sharp edge. Scattered light observations can be fitted with a cavity in small dust that has either a sharp edge at 60 AU, or an edge that transitions smoothly over an annular width of 10 AU near 60 AU. In gas, the data are consistent with a cavity that is smaller, about 15 AU in radius, and whose surface density at 15 AU is $10^{3\pm1}$ times smaller than the surface density at 70 AU; the gas density grades smoothly between these two radii. The CO isotopologue observations rule out a sharp drop in gas surface density at 30 AU or a double-drop model as found by previous modeling. Future observations are needed to assess the nature of these gas and dust cavities, e.g., whether they are opened by multiple as-yet-unseen planets or photoevaporation.
We present the results of a systematic search for Lyman-alpha emitters (LAEs) at $6 \lesssim z \lesssim 7.6$ using the HST WFC3 Infrared Spectroscopic Parallel (WISP) Survey. Our total volume over this redshift range is $\sim 8 \times10^5$ Mpc$^3$, comparable to many of the narrowband surveys despite their larger area coverage. We find two LAEs at $z=6.38$ and $6.44$ with line luminosities of L$_{\mathrm{Ly}\alpha} \sim 4.7 \times 10^{43}$ erg s$^{-1}$, putting them among the brightest LAEs discovered at these redshifts. Taking advantage of the broad spectral coverage of WISP, we are able to rule out almost all lower-redshift contaminants. The WISP LAEs have a high number density of $7.7\times10^{-6}$ Mpc$^{-3}$. We argue that the LAEs reside in Mpc-scale ionized bubbles that allow the Lyman-alpha photons to redshift out of resonance before encountering the neutral IGM. We discuss possible ionizing sources and conclude that the observed LAEs alone are not sufficient to ionize the bubbles.
The effect of baryons on the matter power spectrum is likely to have an observable effect for future galaxy surveys, like Euclid or LSST. As a first step towards a fully predictive theory, we investigate the effect of non-radiative hydrodynamics on the structure of galaxy groups sized halos, which contribute the most to the weak lensing power spectrum. We perform high resolution (more than one million particles per halo and one kilo-parsec resolution) non-radiative hydrodynamical zoom-in simulations of a sample of 16 halos, comparing the profiles to popular analytical models. We find that the total mass profile is well fitted by a Navarro, Frenk & White model, with parameters slightly modified from the dark matter only simulation. We also find that the Komatsu & Seljak hydrostatic solution provides a good fit to the gas profiles, with however significant deviations, arising from strong turbulent mixing in the core and from non-thermal, turbulent pressure support in the outskirts. The turbulent energy follows a shallow, rising linear profile with radius, and correlates with the halo formation time. Using only three main structural halo parameters as variables (total mass, concentration parameter and central gas density), we can predict with an accuracy better than 20% the individual gas density and temperature profiles. For the average total mass profile, which is relevant for power spectrum calculations, we even reach an accuracy of 1%. The robustness of these predictions has been tested against resolution effects, different types of initial conditions and hydrodynamical schemes.
The similarity of the host galaxy of FRB 121102 with those of long gamma-ray bursts and Type I super-luminous supernovae suggests that this FRB could be associated with a young magnetar. By assuming the FRB emission to be produced in the magnetosphere, we derive a lower limit on the age of the magnetar by enabling GHz emission freely escape from the dense relativistic wind of the magnetar. Another lower limit is also obtained by requiring the dispersion measure contributed by the wind electrons/positrons to be consistent with the observations of host galaxy. The energy sources of the FRB and the recently-discovered steady radio counterpart are not clear. As one possibility, these emission components could be powered by the rotational energy of the magnetar. If this is true, then the magnetar cannot be too old. These lower and upper limits on the magnetar age can provide stringent constraints on the emission models of the FRB as well as the steady radio counterpart. Additionally, it is also indicated that the FRB observations can be used to probe the physics of magnetar wind.
Although the cusp-core controversy for dwarf galaxies is seen as a problem, I argue that the cored central profiles can be explained by flattened cusps because they suffer from conflicting measurements and poor statistics and because there is a large number of conventional processes that could have flattened them since their creation, none of which requires new physics. Other problems, such as "too big to fail", are not discussed.
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