Phosphorus is a crucial element in biochemistry, especially the P-O bond, which is key for the formation of the backbone of the deoxyribonucleic acid. So far, PO has only been detected towards the envelope of evolved stars, and never towards star-forming regions. We report the first detection of PO towards two massive star-forming regions, W51 e1/e2 and W3(OH), using data from the IRAM 30m telescope. PN has also been detected towards the two regions. The abundance ratio PO/PN is 1.8 and 3 for W51 and W3(OH), respectively. Our chemical model indicates that the two molecules are chemically related and are formed via gas-phase ion-molecule and neutral-neutral reactions during the cold collapse. The molecules freeze out onto grains at the end of the collapse and desorb during the warm-up phase once the temperature reaches 35 K. Similar abundances of the two species are expected during a period of 5x10^{4} yr at the early stages of the warm-up phase, when the temperature is in the range 35-90 K. The observed molecular abundances of 10^{-10} are predicted by the model if a relatively high initial abundance of 5x10^{-9} of depleted phosphorus is assumed.
We perform zoom-in cosmological simulations of a suite of dwarf galaxies, examining the impact of cosmic-rays generated by supernovae, including the effect of diffusion. We first look at the effect of varying the uncertain cosmic ray parameters by repeatedly simulating a single galaxy. Then we fix the comic ray model and simulate five dwarf systems with virial masses range from 8-30 $\times 10^{10}$ Msun. We find that including cosmic ray feedback (with diffusion) consistently leads to disk dominated systems with relatively flat rotation curves and constant star formation rates. In contrast, our purely thermal feedback case results in a hot stellar system and bursty star formation. The CR simulations very well match the observed baryonic Tully-Fisher relation, but have a lower gas fraction than in real systems. We also find that the dark matter cores of the CR feedback galaxies are cuspy, while the purely thermal feedback case results in a substantial core.
The dust emissivity spectral index, $\beta$, is a critical parameter for deriving the mass and temperature of star-forming structures, and consequently their gravitational stability. The $\beta$ value is dependent on various dust grain properties, such as size, porosity, and surface composition, and is expected to vary as dust grains evolve. Here we present $\beta$, dust temperature, and optical depth maps of the star-forming clumps in the Perseus Molecular Cloud determined from fitting SEDs to combined Herschel and JCMT observations in the 160 $\mu$m, 250 $\mu$m, 350 $\mu$m, 500 $\mu$m, and 850 $\mu$m bands. Most of the derived $\beta$, and dust temperature values fall within the ranges of 1.0 - 2.7 and 8 - 20 K, respectively. In Perseus, we find the $\beta$ distribution differs significantly from clump to clump, indicative of grain growth. Furthermore, we also see significant, localized $\beta$ variations within individual clumps and find low $\beta$ regions correlate with local temperature peaks, hinting at the possible origins of low $\beta$ grains. Throughout Perseus, we also see indications of heating from B stars and embedded protostars, as well evidence of outflows shaping the local landscape.
The study of carbon and oxygen abundances yields information on the time
evolution and nucleosynthetic origins of these elements, yet remains relatively
unexplored. At low metallicities (12+log(O/H) < 8.0), nebular carbon
measurements are limited to rest-frame UV collisionally excited emission lines.
Therefore, we present UV spectrophotometry of 12 nearby, low-metallicity,
high-ionization HII regions in dwarf galaxies obtained with the Cosmic Origins
Spectrograph on the Hubble Space Telescope. We present the first analysis of
the C/O ratio in local galaxies based solely on simultaneous significant
detections of the UV O^+2 and C^+2 collisionally excited lines in seven of our
targets and five objects from the literature, to create a final sample of 12
significant detections. Our sample is complemented by optical SDSS spectra,
from which we measured the nebular physical conditions and oxygen abundances
using the direct method.
At low metallicity (12+log(O/H) < 8.0), no clear trend is evident in C/O vs.
O/H for the present sample given the large dispersion observed. When combined
with recombination line observations at higher values of O/H, a general trend
of increasing C/O with increasing O/H is also viable, but with some significant
outliers. Additionally, we find the C/N ratio appears to be constant (but with
significant scatter) over a large range in oxygen abundance, indicating carbon
is predominantly produced by similar nucleosynthetic mechanisms as nitrogen. If
true, and our current understanding of nitrogen production is correct, this
would indicate that primary production of carbon (a flat trend) dominates at
low metallicity, but quasi-secondary production (an increasing trend) becomes
prominent at higher metallicities. A larger sample will be needed to determine
the true nature and dispersion of the relation.
We analyse structural decompositions of 500 late-type galaxies (Hubble $T$-type $\ge 6$) from the Spitzer Survey of Stellar Structure in Galaxies (S$^4$G), spanning a stellar mass range of about $10^7$ to a few times $10^{10}$ M$_\odot$. Their decomposition parameters are compared with those of the early-type dwarfs in the Virgo cluster from Janz et al. They have morphological similarities, including the fact that the fraction of simple one-component galaxies in both samples increases towards lower galaxy masses. We find that in the late-type two-component galaxies both the inner and outer structures are by a factor of two larger than those in the early-type dwarfs, for the same stellar mass of the component. While dividing the late-type galaxies to low and high density environmental bins, it is noticeable that both the inner and outer components of late types in the high local galaxy density bin are smaller, and lie closer in size to those of the early-type dwarfs. This suggests that, although structural differences between the late and early-type dwarfs are observed, environmental processes can plausibly transform their sizes sufficiently, thus linking them evolutionarily.
We present a precise optical and near-infrared determination of the Tip of the Red Giant Branch (TRGB) brightness in the Large and Small Magellanic Clouds (respectively LMC and SMC). The commonly used calibrations of the absolute magnitude of the TRGB lead to an overestimation of the distance to the LMC and SMC in the K band, and an underestimation of the distance in the optical I band for both galaxies. Reported discrepancies are at the level of 0.2 mag, with respect to the very accurate distance determinations to both Clouds based on late-type eclipsing binaries. The differential distances between the LMC and SMC obtained in the J and K bands, and for the bolometric brightness are consistent with each other, and with the results obtained from eclipsing binaries and other distance indicators.
We investigate the dust energy balance for the edge-on galaxy IC 2531, one of the seven galaxies in the HEROES sample. We perform a state-of-the-art radiative transfer modelling based, for the first time, on a set of optical and near-infrared galaxy images. We show that taking into account near-infrared imaging in the modelling significantly improves the constraints on the retrieved parameters of the dust content. We confirm the result from previous studies that including a young stellar population in the modelling is important for explaining the observed stellar energy distribution. However, the discrepancy between the observed and modelled thermal emission at far-infrared wavelengths, the so-called dust energy balance problem, is still present: the model underestimates the observed fluxes by a factor of about two. We compare two different dust models, and find that dust parameters and thus the spectral energy distribution in the infrared domain are sensitive to the adopted dust model. In general, the THEMIS model reproduces the observed emission in the infrared wavelength domain better than the popular Zubko et al. BARE-GR-S model. Our study of IC 2531 is a pilot case for detailed and uniform radiative transfer modelling of the entire HEROES sample, which will shed more light on the strength and origins of the dust energy balance problem.
In the last decade, using single epoch virial based techniques in the optical band, it has been possible to measure the central black hole mass on large AGN1 samples. However these measurements use the width of the broad line region as a proxy of the virial velocities and are therefore difficult to be carried out on those obscured (type 2) or low luminosity AGN where the nuclear component does not dominate in the optical. Here we present the optical and near infrared spectrum of the starburst/Seyfert galaxy NGC 6221, observed with X-shooter/VLT. Previous observations of NGC 6221 in the X-ray band show an absorbed (N_H=8.5 +/- 0.4 x 10^21 cm^-2) spectrum typical of a type 2 AGN with luminosity log(L_14-195 keV) = 42.05 erg/s, while in the optical band its spectrum is typical of a reddened (A_V=3) starburst. Our deep X-shooter/VLT observations have allowed us to detect faint broad emission in the H_alpha, HeI and Pa_beta lines (FWHM ~1400-2300 km/s) confirming previous studies indicating that NGC 6221 is a reddened starburst galaxy which hosts an AGN. We use the measure of the broad components to provide a first estimate of its central black hole mass (M_BH = 10^(6.6 +/- 0.3) Msol, lambda_Edd=0.01-0.03), obtained using recently calibrated virial relations suitable for moderately obscured (N_H<10^24 cm^-2) AGN.
We present two new examples of galaxies undergoing transformation in the Shapley supercluster core. These low-mass (stellar mass from 0.4E10 to 1E10 Msun) galaxies are members of the two clusters SC-1329-313 (z=0.045) and SC-1327-312 (z=0.049). Integral-field spectroscopy complemented by imaging in ugriK bands and in Halpha narrow-band are used to disentangle the effects of tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies, SOS-61086 and SOS-90630, we observe one-sided extraplanar ionized gas extending respectively 30kpc and 41kpc in projection from their disks. The galaxies' gaseous disks are truncated and the kinematics of the stellar and gas components are decoupled, supporting the RPS scenario. The emission of the ionized gas extends in the direction of a possible companion for both galaxies suggesting a TI. The overall gas velocity field of SOS-61086 is reproduced by ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and starting about 250Myr ago, consistent with the age of the young stellar populations. A link between the observed gas stripping and the cluster-cluster interaction experienced by SC-1329-313 and A3562 is suggested. Simulations of ram pressure acting almost edge-on are able to fully reproduce the gas velocity field of SOS-90630, but cannot at the same time reproduce the extended tail of outflowing gas. This suggests that an additional disturbance from a TI is required. This study adds a piece of evidence that RPS may take place in different environments with different impacts and witnesses the possible effect of cluster-cluster merger on RPS.
The determination of galaxy redshifts in James Webb Space Telescope (JWST)'s blank-field surveys will mostly rely on photometric estimates, based on the data provided by JWST's Near-Infrared Camera (NIRCam) at 0.6-5.0 {\mu}m and Mid Infrared Instrument (MIRI) at {\lambda}>5.0 {\mu}m. In this work we analyse the impact of choosing different combinations of NIRCam and MIRI broad-band filters (F070W to F770W), as well as having ancillary data at {\lambda}<0.6 {\mu}m, on the derived photometric redshifts (zphot) of a total of 5921 real and simulated galaxies, with known input redshifts z=0-10. We found that observations at {\lambda}<0.6 {\mu}m are necessary to control the contamination of high-z samples by low-z interlopers. Adding MIRI (F560W and F770W) photometry to the NIRCam data mitigates the absence of ancillary observations at {\lambda}<0.6 {\mu}m and improves the redshift estimation, both reducing the fraction of high-z contaminants and preventing the leakage of high-z sources towards low z. At z=7-10, accurate zphot can be obtained with the NIRCam broad bands alone when S/N>=10, but the zphot quality significantly degrades at S/N<=5. Adding MIRI photometry with one magnitude brighter depth than the NIRCam depth allows for a redshift recovery of 83-99%, depending on SED type, and its effect is particularly noteworthy for galaxies with nebular emission. The vast majority of NIRCam galaxies with [F150W]=29 AB mag at z=7-10 will be detected with MIRI at [F560W, F770W]<28 mag if these sources are at least mildly evolved or have spectra with emission lines boosting the mid-infrared fluxes.
Using a specialized technique sensitive to the presence of expanding ionized gas we have detected a set of three concentric expanding shells in an HII region in the nearby spiral galaxy M33. After mapping the kinematics in H{\alpha} with Fabry-Perot spectroscopy we used slit spectra to measure the intensities of the [SII] doublet at {\lambda}{\lambda} 671.9, 673.1 nm and the [NII] doublet at {\lambda}{\lambda} 645.8, 658.3 nm to corroborate the kinematics and apply diagnostic tests using line ratios. These showed that the expanding shells are shock dominated as would be the case if they had originated with supernova explosions. Estimating their kinetic energies we find fairly low values, indicating a fairly advanced stage of evolution. We obtain density, mass and parent star mass estimates, which, along with the kinetic energies, are inconsistent with the simplest models of shock-interstellar medium interaction. We propose that the presence and properties of an inhomogeneous medium offer a scenario which can account for these observations, and discuss the implications. Comparing our results with data from the literature supports the combined presence of an HII region and supernova remnant material at the observed position.
We investigate the region around the Planck-detected z=3.26 gravitationally lensed galaxy HATLAS J114637.9-001132 (hereinafter HATLAS12-00) using both archival Herschel data from the H-ATLAS survey and using submm data obtained with both LABOCA and SCUBA2. The lensed source is found to be surrounded by a strong overdensity of both Herschel-SPIRE sources and submm sources. We detect 17 bright (S_870 >~7 mJy) sources at >4sigma closer than 5 arcmin to the lensed object at 850/870 microns. Ten of these sources have good cross-identifications with objects detected by Herschel-SPIRE which have redder colours than other sources in the field, with 350 micron flux > 250 micron flux, suggesting that they lie at high redshift. Submillimeter Array (SMA) observations localise one of these companions to ~1 arcsecond, allowing unambiguous cross identification with a 3.6 and 4.5 micron Spitzer source. The optical/near-IR spectral energy distribution (SED) of this source is measured by further observations and found to be consistent with z>2, but incompatible with lower redshifts. We conclude that this system may be a galaxy cluster/protocluster or larger scale structure that contains a number of galaxies undergoing starbursts at the same time.
Line intensity mapping is a superb tool to study the collective radiation from early galaxies. However, the method is hampered by the presence of strong foregrounds, mostly produced by low-redshift interloping lines. We present here a general method to overcome this problem which is robust against foreground residual noise and based on the cross-correlation function $\psi_{\alpha L}(r)$ between diffuse line emission and Ly$\alpha$ emitters (LAE). We compute the diffuse line (Ly$\alpha$ is used as an example) emission from galaxies in a $(800{\rm Mpc})^3$ box at $z = 5.7$ and $6.6$. We divide the box in slices and populate them with $14000(5500)$ LAEs at $z = 5.7(6.6)$, considering duty cycles from $10^{-3}$ to $1$. Both the LAE number density and slice volume are consistent with the expected outcome of the Subaru HSC survey. We add gaussian random noise with variance $\sigma_{\rm N}$ up to 100 times the variance of the Ly$\alpha$ emission, $\sigma_\alpha$, to simulate foregrounds and compute $\psi_{\alpha L}(r)$. We find that the signal-to-noise of the observed $\psi_{\alpha L}(r)$ does not change significantly if $\sigma_{\rm N} \le 10 \sigma_\alpha$ and show that in these conditions the mean line intensity, $I_{Ly\alpha}$, can be precisely recovered independently of the LAE duty cycle. Even if $\sigma_{\rm N} = 100 \sigma_\alpha$, $I_\alpha$ can be constrained within a factor $2$. The method works equally well for any other line (e.g. HI 21 cm, [CII], HeII) used for the intensity mapping experiment.
Images of the linear polarization of synchrotron radiation around Active Galactic Nuclei (AGN) identify their projected magnetic field lines and provide key data for understanding the physics of accretion and outflow from supermassive black holes. The highest resolution polarimetric images of AGN are produced with Very Long Baseline Interferometry (VLBI). Because VLBI incompletely samples the Fourier transform of the source image, any image reconstruction that fills in unmeasured spatial frequencies will not be unique and reconstruction algorithms are required. In this paper, we explore extensions of the Maximum Entropy Method (MEM) to linear polarimetric VLBI imaging. In contrast to previous work, our polarimetric MEM algorithm combines a Stokes I imager that uses only bispectrum measurements that are immune to atmospheric phase corruption with a joint Stokes Q and U imager that operates on robust polarimetric ratios. We demonstrate the effectiveness of our technique on 7- and 3-mm wavelength quasar observations from the VLBA and simulated 1.3-mm Event Horizon Telescope observations of Sgr A* and M87. Consistent with past studies, we find that polarimetric MEM can produce superior resolution compared to the standard CLEAN algorithm when imaging smooth and compact source distributions. As an imaging framework, MEM is highly adaptable, allowing a range of constraints on polarization structure. Polarimetric MEM is thus an attractive choice for image reconstruction with the EHT.
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We continue the exploration of the BaLROG (Bars in Low Redshift Optical Galaxies) sample: 16 large mosaics of barred galaxies observed with the integral field unit SAURON. We quantify the influence of bars on the composition of the stellar component. We derive linestrength indices of H${\beta}$, Fe5015 and Mgb. Based on single stellar population (SSP) models, we calculate ages, metallicities and [Mg/Fe] abundances and their gradients along the bar major and minor axes. The high spatial resolution of our data allows us to identify breaks among index and SSP profiles, commonly at 0.13$\pm$0.06 bar length, consistent with kinematic features. Inner gradients are about ten times steeper than outer gradients and become larger when there is a central rotating component, implying that the gradients are not independent of dynamics and orbits. Central ages appear to be younger for stronger bars. Yet, the bar regions are usually old. We find a flattening of the iron (Fe5015) and magnesium (Mgb) outer gradients along the bar major axis, translating into a flattening of the metallicity gradient. This gradient is found to be 0.03$\pm$0.07 dex/kpc along the bar major axis while the mean value of the bar minor axis compares well with that of an unbarred control sample and is significantly steeper, namely -0.20$\pm$0.04 dex/kpc. These results confirm recent simulations and discern the important localized influence of bars. The elevated [Mg/Fe] abundances of bars and bulges compared to the lower values of discs suggest an early formation, in particular for early type galaxies.
We study the preferred environments of z~0 massive relic galaxies (M_star > 10^10 M_sun galaxies with little or no growth from star formation or mergers since z~2). Significantly, we carry out our analysis on both a large cosmological simulation and an observed galaxy catalogue. Working on the Millennium I-WMAP7 simulation we show that the fraction of today massive objects which have grown less than 10 per cent in mass since z~2 is ~0.04 per cent for the whole massive galaxy population with M_star > 10^10 M_sun. This fraction rises to ~0.18 per cent in galaxy clusters, confirming that clusters help massive galaxies remain unaltered. Simulations also show that massive relic galaxies tend to be closer to cluster centres than other massive galaxies. Using the NYU Value-Added Galaxy Catalogue, and defining relics as M_star > 10^10 M_sun early-type galaxies with colours compatible with single-stellar population ages older than 10 Gyr, and which occupy the bottom 5-percentile in the stellar mass-size distribution, we find 1.11+-0.05 per cent of relics among massive galaxies. This fraction rises to 2.4+-0.4 per cent in high-density environments. Our findings point in the same direction as the works by Poggianti et al. (2013) and Stringer et al. (2015). Our results may reflect the fact that the cores of the clusters are created very early on, hence the centres host the first cluster members. Near the centres, high velocity dispersions and harassment help cluster core members avoid the growth of an accreted stellar envelope via mergers, while a hot intracluster medium prevents cold gas from reaching the galaxies, inhibiting star formation.
Using a sample of dwarf irregular galaxies selected from the ALFALFA blind HI-survey and observed using the VIMOS IFU, we investigate the relationship between H$\alpha$ emission and Balmer optical depth ($\tau_{\text{b}}$). We find a positive correlation between H$\alpha$ luminosity surface density and Balmer optical depth in 8 of 11 at $\geq$ 0.8$\sigma$ significance (6 of 11 at $\geq$ 1.0$\sigma$) galaxies. Our spaxels have physical scales ranging from 30 to 80 pc, demonstrating that the correlation between these two variables continues to hold down to spatial scales as low as 30 pc. Using the Spearman's rank correlation coefficient to test for correlation between $\Sigma_{\text{H}\alpha}$ and $\tau_{\text{b}}$ in all the galaxies combined, we find $\rho = 0.39$, indicating a positive correlation at 4$\sigma$ significance. Our low stellar-mass galaxy results are in agreement with observations of emission line regions in larger spiral galaxies, indicating that this relationship is independent of the size of the galaxy hosting the emission line region. The positive correlation between H$\alpha$ luminosity and Balmer optical depth within spaxels is consistent with the hypothesis that young star-forming regions are surrounded by dusty birth-clouds.
The intrinsic escape fraction of ionizing Lyman continuum photons ($f_{esc}$) is crucial to understand whether galaxies are capable of reionizing the neutral hydrogen in the early universe at z>6. Unfortunately, it is not possible to access $f_{esc}$ at z>4 with direct observations and the handful of measurements from low redshift galaxies consistently find $f_{esc}$ < 10%, while at least $f_{esc}$ ~ 10% is necessary for galaxies dominate reionization. Here, we present the first empirical prediction of $f_{esc}$ at z>6 by combining the (sparsely populated) relation between [OIII]/[OII] and $f_{esc}$ with the redshift evolution of [OIII]/[OII] as predicted from local high-z analogs selected by their H$\alpha$ equivalent-width. We find $f_{esc}$ = $5.7_{-3.3}^{+8.3}$% at z=6 and $f_{esc}$ = $10.4_{-6.3}^{+15.5}$% at z=9 for galaxies with log(M/M$_{sun}$) ~ 9.0 (errors given as 1$\sigma$). However, there is a negative correlation with stellar mass and we find up to 50% larger $f_{esc}$ per 0.5 dex decrease in stellar mass. The population averaged escape fraction increases according to $f_{esc}$ = $f_{esc,0} ((1+z)/3)^a$, with $f_{esc,0} = 2.3 \pm 0.05$% and $a=1.17 \pm 0.02$ at z > 2 for log(M/M$_{sun}$) ~ 9.0. With our empirical prediction of $f_{esc}$ (thus fixing an important previously unknown variable) and further reasonable assumption on clumping factor and the production efficiency of Lyman continuum photons, we conclude that the average population of galaxies is just capable to reionize the universe by z ~ 6.
The outer stellar halos of galaxies contain vital information about the formation history of galaxies, since the relaxation timescales in the outskirts are long enough to keep the memory, while the information about individual formation events in the central parts has long been lost due to mixing, star formation and relaxation. To unveil some of the information encoded in these faint outer halo regions, we study the stellar outskirts of galaxies selected from a fully hydrodynamical high resolution cosmological simulation, called Magneticum. We find that the density profiles of the outer stellar halos of galaxies over a broad mass range can be well described by an Einasto profile. For a fixed total mass range, the free parameters of the Einasto fits are closely correlated. Galaxies which had more (dry) merger events tend to have lesser curved outer stellar halos, however, we find no indication that the amount of curvature is correlated with galaxy morphology. The Einasto-like shape of the outer stellar halo densities can also explain the observed differences between the Milky Way and Andromeda outer stellar halos.
We present the results from a systematic search for galactic-scale, molecular (OH 119 $\mu$m) outflows in a sample of 52 Local Volume ($d < 50$ Mpc) Burst Alert Telescope detected active galactic nuclei (BAT AGN) with \emph{Herschel}-PACS. We combine the results from our analysis of the BAT AGN with the published \emph{Herschel}/PACS data of 43 nearby ($z<0.3$) galaxy mergers, mostly ultraluminous infrared galaxies (ULIRGs) and QSOs. The objects in our sample of BAT AGN have, on average, $\sim 10-100$ times lower AGN luminosities, star formation rates (SFRs), and stellar masses than those of the ULIRG and QSO sample. OH 119 $\mu$m is detected in 42 of our BAT AGN targets. Evidence for molecular outflows (i.e. OH absorption profiles with median velocities more blueshifted than $-$50 km s$^{-1}$ and/or blueshifted wings with 84-percentile velocities less than $-$300 km s$^{-1}$) is seen in only four BAT AGN (NGC~7479 is the most convincing case). Evidence for molecular inflows (i.e. OH absorption profiles with median velocities more redshifted than 50 km s$^{-1}$) is seen in seven objects, although an inverted P-Cygni profile is detected unambiguously in only one object (Circinus). Our data show that both the starburst and AGN contribute to driving OH outflows, but the fastest OH winds require AGN with quasar-like luminosities. We also confirm that the total absorption strength of OH 119 $\mu$m is a good proxy for dust optical depth as it correlates strongly with the 9.7 $\mu$m silicate absorption feature, a measure of obscuration originating in both the nuclear torus and host galaxy disk.
Galaxies at high redshifts provide a valuable tool to study cosmic dawn, and therefore it is crucial to reliably identify these galaxies. Here, we present an unambiguous and first simultaneous detection of both the Lyman-\alpha emission and the Lyman break from a z = 7.512+/- 0.004 galaxy, observed in the Faint Infrared Grism Survey (FIGS). These spectra, taken with G102 grism on Hubble Space Telescope (HST), show a significant emission line detection (6{\sigma}) in multiple observational position angles (PA), with total integrated Ly{\alpha} line flux of 1.06+/- 0.12 e10-17erg s-1cm-2. The line flux is nearly a factor of four higher than the previous MOSFIRE spectroscopic observations of faint Ly{\alpha} emission at {\lambda} = 1.0347{\mu}m, yielding z = 7.5078+/- 0.0004. This is consistent with other recent observations implying that ground-based near-infrared spectroscopy underestimates total emission line fluxes, and if confirmed, can have strong implications for reionization studies that are based on ground-based Lyman-{\alpha} measurements. A 4-{\sigma} detection of the NV line in one PA also suggests a weak Active Galactic Nucleus (AGN), potentially making this source the highest-redshift AGN yet found. Thus, this observation from the Hubble Space Telescope clearly demonstrates the sensitivity of the FIGS survey, and the capability of grism spectroscopy to study the epoch of reionization.
The Frontier Fields are a director's discretionary time campaign with HST and the Spitzer Space Telescope to see deeper into the universe than ever before. The Frontier Fields combine the power of HST and Spitzer with the natural gravitational telescopes of massive high-magnification clusters of galaxies to produce the deepest observations of clusters and their lensed galaxies ever obtained. Six clusters - Abell 2744, MACSJ0416.1-2403, MACSJ0717.5+3745, MACSJ1149.5+2223, Abell S1063, and Abell 370 - were selected based on their lensing strength, sky darkness, Galactic extinction, parallel field suitability, accessibility to ground-based facilities, HST, Spitzer and JWST observability, and pre-existing ancillary data. These clusters have been targeted by the HST ACS/WFC and WFC3/IR with coordinated parallels of adjacent blank fields for over 840 HST orbits. The Spitzer Space Telescope has dedicated > 1000 hours of director's discretionary time to obtain IRAC 3.6 and 4.5 micron imaging to ~26.5, 26.0 ABmag 5-sigma point-source depths in the six cluster and six parallel Frontier Fields. The Frontier Field parallel fields are the second-deepest observations thus far by HST with ~29th ABmag 5-sigma point source depths in seven optical - near-infrared bandpasses. Galaxies behind the Frontier Field cluster lenses experience typical magnification factors of a few, with small regions near the critical curves magnified by factors 10-100. Therefore, the Frontier Field cluster HST images achieve intrinsic depths of ~30-33 magnitudes over very small volumes. Early studies of the Frontier Fields have probed galaxies fainter than any seen before during the epoch of reionization 6 < z < 10, mapped out the cluster dark matter to unprecedented resolution, and followed lensed transient events.
Continuing with previous research (Camperi et al. 2011),new heliocentric radial velocity distributions are presented for the nearby galaxy NGC 253, obtained from the ionized hydrogen recombination line H-alpha. These distributions have been derived from long-slit spectroscopy for various position angles. It is also shown the heliocentric radial velocity distribution corresponding to part of the infrared data (ionized hydrogen recombination line Br-gamma) observed with the Phoenix spectrograph of the Gemini South Observatory. Sequential mapping with the long slit using this instrument will enable to study in detail the kinematics of the galaxy's core, which is strongly obscured by dust.
We report the detection, using observations of the CO(2-1) line performed with the Atacama Pathfinder EXperiment, of molecular gas in the region of the outer filament of Centaurus A, a complex region known to show various signatures of an interaction between the radio jet, an HI cloud and ionised gas filaments. We detect CO(2-1) at all observed locations, which were selected to represent regions with very different physical conditions. The H_2 masses of the detections range between 0.2 x 10^6 and 1.1 x 10^6 msun, for conservative choices of the CO-to-H_2 conversion factor. Surprisingly, the stronger detections are not coincident with the HI cloud, but instead are in the region of the ionised filaments. We also find variations in the widths of the CO(2-1) lines throughout the region, with broader lines in the region of the ionised gas, i.e. where the jet-cloud interaction is strongest, and narrow profiles in the HI cloud. This may indicate that the molecular gas in the region of the ionised gas has the momentum of the jet-cloud interaction encoded in it, in a similar way as the ionised gas. These molecular clouds may therefore be the result of very efficient cooling of the down-stream gas photo/shock-ionised by the interaction. On the other hand, the molecular clouds with narrower profiles, which are closer to or inside the HI cloud, could be pre-existing cold H_2 cores which manage to survive the effects of the passing jet.
We combine a semi-analytic model of galaxy evolution with constraints on circumstellar habitable zones and the distribution of terrestrial planets to probe the suitability of galaxies of different mass and type to host habitable planets, as well as its evolution with time. We find that the fraction of stars with terrestrial planets in their habitable zone ("habitability") depends only weakly on galaxy mass, with a maximum around 4e10 Msun. We estimate that 0.7% of all stars in Milky Way type galaxies to host a terrestrial planet within their habitable zone, consistent with the value derived from Kepler observations. On the other hand, the habitability of passive galaxies is slightly but systematically higher, unless we assume an unrealistically high sensitivity of planets to supernovae. We find that the overall habitability of galaxies has not changed significantly in the last ~8 Gyr, with most of the habitable planets in local disk galaxies having formed ~1.5 Gyr before our own solar system. Finally, we expect that ~1.4e9 planets similar to present-day Earth have existed so far in our galaxy.
The quantization of energy levels in very nanoparticles suppresses dissipative processes that convert grain rotational kinetic energy into heat. For grains small enough to have GHz rotation rates, the suppression of dissipation can be extreme. As a result, alignment of such grains is suppressed. This applies both to alignment of the grain body with its angular momentum J, and to alignment of J with the local magnetic field B_0. If the anomalous microwave emission is rotational emission from spinning grains, it will be negligibly polarized at GHz frequencies, with P < 10^{-6} at frequencies above 10 GHz.
We present a catalogue of 1715 early-type galaxies from the literature, spanning the luminosity range from faint dwarf spheroidal galaxies to giant elliptical galaxies. The aim of this catalogue is to be one of the most comprehensive and publicly available collections of data on early-type galaxies. The emphasis in this catalogue lies on dwarf elliptical galaxies, for which some samples with detailed data have been published recently. For almost all of the early-type galaxies included in it, this catalogue contains data on their locations, distances, redshifts, half-light radii, the masses of their stellar populations and apparent magnitudes in various passbands. Data on metallicity and various colours are available for a majority of the galaxies presented here, including many of the rather faint early-type galaxies in the Local group. The data on magnitudes, colours, metallicities and masses of the stellar populations is supplemented with entries that are based on fits to data from simple stellar population models and existing data from observations. Also, some simple transformations have been applied to the data on magnitudes, colours and metallicities in this catalog, in order to increase the homogeneity of this data. Estimates on the S\'{e}rsic profiles, internal velocity dispersions, maximum rotational velocities, dynamical masses and ages are listed for several hundreds of the galaxies in this catalogue. Finally, each quantity listed in this catalogue is accompanied with information on its source, so that users of this catalogue can easily exclude data that they do not consider as reliable enough for their purposes.
We present results of our study on eight dense cores, previously classified as starless, using infrared (3-160 {\micron}) imaging observations with \textit{AKARI} telescope and molecular line (HCN and N$_2$H$^+$) mapping observations with \textit{KVN} telescope. Combining our results with the archival IR to mm continuum data, we examined the starless nature of these eight cores. Two of the eight cores are found to harbor faint protostars having luminosity of $\sim0.3-4.4$ L$_{\odot}$. The other six cores are found to remain as starless and probably are in a dynamically transitional state. The temperature maps produced using multi-wavelength images show an enhancement of about 3-6 K towards the outer boundary of these cores, suggesting that they are most likely being heated externally by nearby stars and/or interstellar radiation fields. Large virial parameters and an over-dominance of red asymmetric line profiles over the cores may indicate that the cores are set into either an expansion or an oscillatory motion, probably due to the external heating. Most of the starless cores show coreshine effect due to the scattering of light by the micron-size dust grains. This may imply that the age of the cores is of the order of $\sim10^{5}$ years, being consistent with the timescale required for the cores to evolve into an oscillatory stage due to the external perturbation. Our observational results support the idea that the external feedback from nearby stars and/or interstellar radiation fields may play an important role in the dynamical evolution of the cores.
The paper is a brief overview of the works by Iosif S. Shklovsky
(1916--1985), carried out over almost 30 years (1955--1985), on the nature of
activity (primarily in the radio frequency range) in nuclei of some galaxies.
Worthy of note is Shklovsky's pioneering work of 1962, in which he made an
attempt to consider possible evolutionary tracks of extragalactic radio sources
by constructing an analog of the Herzsprung--Russel diagram for stars (radio
luminosity at 160 MHz was taken instead of optical luminosity; total radio size
at the same frequency, as the other parameter). Later works by other authors
are also discussed, where similar diagrams were plotted using a larger
observational material.
Special attention is paid to the evolution of Shklovsky's views regarding the
possible ways of gas getting into radio galaxies' central regions, followed by
high-velocity ejections of magnetized plasmons from their nuclei. In his
assumptions, Shklovsky was mainly based on the observational data for the
properties of the closest radio galaxy, NGC 4486 (Virgo A, M87), which he
believed to be the same reference standard for extragalactic radio astronomy as
the Crab Nebula for galactic radio astronomy.
Shklovsky's approach to the recurrence of the activity phenomenon in galactic
nuclei and the one-sided character of radio ejections from them is discussed.
Modern views on these issues are also briefly considered.
We investigate the dust properties in three spectroscopically anomalous galaxies (IRAS F10398+1455, IRAS F21013-0739 and SDSS J0808+3948). Their Spitzer/IRS spectra are characterized by a steep ~5-8 micron emission continuum, strong emission bands from polycyclic aromatic hydrocarbon (PAH) molecules, and prominent 10 micron silicate emission. The steep ~5-8 micron continuum and strong PAH emission features suggest the presence of starbursts, while the silicate emission is indicative of significant heating from AGNs. The simultaneous detection of these two observational properties has rarely been reported on galactic scale. We employ the PAHFIT software to estimate their starlight contributions, and the CLUMPY model for the components contributed by the AGN tori. We find that the CLUMPY model is generally successful in explaining the overall dust infrared emission, although it appears to emit too flat at the ~5-8 micron continuum to be consistent with that observed in IRAS F10398+1455 and IRAS F21013-0739. The flat ~5-8 micron continuum calculated from the CLUMPY model could arise from the adopted specific silicate opacity of Ossenkopf et al. (1992) which exceeds that of the Draine & Lee (1984) "astronomical silicate" by a factor up to 2 in the ~5-8 micron wavelength range. Future models with a variety of dust species incorporated in the CLUMPY radiation transfer regime are needed for a thorough understanding of the dust properties of these spectroscopically anomalous galaxies.
Ices play a critical role during the evolution of interstellar clouds. Their presence is ubiquitous in the dense molecular medium and their impact is not only limited to chemistry. Species adsorbed onto dust grains also affect cloud thermodynamics. It all depends on the interstellar conditions, the chemical parameters, and the composition of ice layers. In this work, I study the formation of ices by focusing on the interplay between gas and solid phase to determine their role on cloud evolution and star formation. I show that while the formation of ices greatly impacts the cloud chemistry, their role on the thermodynamics is more conservative, and their influence on star formation is only marginal.
We present results from a 90 ks Chandra ACIS-S observation of the X-ray luminous interacting galaxy system Arp 299 (NGC 3690/IC 694). We detect 25 discrete X-ray sources with luminosities above 4.0x10^38 erg s^-1 covering the entire Ultra Luminous X-ray source (ULX) regime. Based on the hard X-ray spectra of the non-nuclear discrete sources identified in Arp 299, and their association with young, actively star-forming region of Arp 299 we identify them as HMXBs. We find in total 20 off-nuclear sources with luminosities above the ULX limit, 14 of which are point-like sources. Furthermore we observe a marginally significant deficit in the number of ULXs, with respect to the number expected from scaling relations of X-ray binaries with the star formation rate (SFR). Although the high metalicity of the galaxy could result in lower ULX numbers, the good agreement between the observed total X-ray luminosity of ULXs, and that expected from the relevant scaling relation indicates that this deficit could be the result of confusion effects. The integrated spectrum of the galaxy shows the presence of a hot gaseous component with kT = 0.72+-0.03 keV, contributing 20% of the soft (0.1-2.0 keV) unabsorbed luminosity of the galaxy. A plume of soft X-ray emission in the west of the galaxy indicates a large scale outflow. We find that the AGN in NGC 3690 contributes only 22% of the observed broad-band X-ray luminosity of Arp 299.
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical models based on Blandford & Znajek extract the rotational energy from a Kerr black hole, which could be the case for NGC1052, to launch these jets. This requires magnetic fields of the order of $10^3\,$G to $10^4\,$G. We imaged the vicinity of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature, smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the magnetic field at 1 Schwarzschild radius to lie between 200 G and ~80000 G consistent with Blandford & Znajek models.
We present an argument that radio galaxies (active galaxies with mis-aligned jets) are likely to be the primary sources of the high-energy astrophysical neutrinos observed by IceCube. In particular, if the gamma-ray emission observed from radio galaxies is generated through the interactions of cosmic-ray protons with gas, these interactions can also produce a population of neutrinos with a flux and spectral shape similar to that measured by IceCube. We present a simple physical model in which high-energy cosmic rays are confined within the volumes of radio galaxies, where they interact with gas to generate the observed diffuse fluxes of neutrinos and gamma rays. In addition to simultaneously accounting for the observations of Fermi and IceCube, radio galaxies in this model also represent an attractive class of sources for the highest energy cosmic rays.
We constrain the internal dynamics of a stack of 10 clusters from the GCLASS survey at 0.87<z<1.34. We determine the stack cluster mass profile M(r) using the MAMPOSSt algorithm of Mamon et al., the velocity anisotropy profile beta(r) from the inversion of the Jeans equation, and the pseudo-phase-space density profiles Q(r) and Qr(r), obtained from the ratio between the mass density profile and the third power of the (total and, respectively, radial) velocity dispersion profiles of cluster galaxies. Several M(r) models are statistically acceptable for the stack cluster (Burkert, Einasto, Hernquist, NFW). The total mass distribution has a concentration c=r200/r-2=4.0-0.6+1.0, in agreement with theoretical expectations, and is less concentrated than the cluster stellar-mass distribution. The stack cluster beta(r) is similar for passive and star-forming galaxies and indicates isotropic galaxy orbits near the cluster center and increasingly radially elongated with increasing cluster-centric distance. Q(r) and Qr(r) are almost power-law relations with slopes similar to those predicted from numerical simulations of dark matter halos. Combined with results obtained for lower-z clusters we determine the dynamical evolution of galaxy clusters, and compare it with theoretical predictions. We discuss possible physical mechanisms responsible for the differential evolution of total and stellar mass concentrations, and of passive and star-forming galaxy orbits [abridged].
Millimeter observations of CO isotopologues are often used to make inferences about protoplanetary disk gas density and temperature structures. The accuracy of these estimates depends on our understanding of CO freezeout and desorption from dust grains. Most models of these processes indicate that CO column density decreases monotonically with distance from the central star due to a decrease in gas density and freezeout beyond the CO snowline. We present ALMA Cycle 2 observations of $^{12}$CO, $^{13}$CO, and C$^{18}$O $J=2-1$ emission that instead suggest CO enhancement in the outer disk of T Tauri star AS 209. Most notably, the C$^{18}$O emission consists of a central peak and a ring at a radius of $\sim1''$ (120 AU), well outside the expected CO snowline. We propose that the ring arises from the onset of CO desorption near the edge of the millimeter dust disk. CO desorption exterior to a CO snowline may occur via non-thermal processes involving cosmic rays or high-energy photons, or via a radial thermal inversion arising from dust migration.
The image subtraction technique applied to study variable stars in globular clusters represented a leap in the number of new detections, with the drawback that many of these new light curves could not be transformed to magnitudes due to the severe crowding. In this paper we present observations of four Galactic globular clusters, M 2 (NGC 7089), M 10 (NGC 6254), M 80 (NGC 6093) and NGC 1261, taken with the ground-layer adaptive optics module at the SOAR Telescope, SAM. We show that the higher image quality provided by SAM allows the calibration of the light curves of the great majority of the variables near the cores of these clusters as well as the detection of new variables even in clusters where image-subtraction searches were already conducted. We report the discovery of 15 new variables in M 2 (12 RR Lyrae stars and 3 SX Phe stars), 12 new variables in M 10 (11 SX Phe and one long-period variable) and one new W UMa-type variable in NGC 1261. No new detections are found in M 80, but previous uncertain detections are confirmed and the corresponding light curves are calibrated into magnitudes. Additionally, based on the number of detected variables and new HST/UVIS photometry, we revisit a previous suggestion that M 80 may be the globular cluster with the richest population of blue stragglers in our Galaxy.
We study the effect of Active Nuclei Galaxy (AGN) feedback as one of the major mechanisms modifying the cluster morphology influencing scaling relations, which are the most uncertain factor in constraining cosmology with clusters of galaxies. Using cosmological hydrodynamical simulations we investigate how the AGN feedback changes the X-ray morphology of the simulated systems, and compare to the observed REXCESS (Representative XMM-Newton Cluster Structure Survey) clusters. We apply centre shifts and power ratios to characterise the cluster morphology, and find that our simulated clusters are more substructured than the observed ones. We show that the degree of this discrepancy is affected by the inclusion of AGN feedback. While the clusters simulated with the AGN feedback are in much better agreement with the REXCESS L_X-T relation, they are also more substructured, which increases the tension with observations. This suggests that not only global cluster properties such as L_X and T and radial profiles should be used to compare and to calibrate simulations with observations, but also substructure measures such as centre shifts and power ratios. We discuss what changes in the simulations might ease the tension with observational constraints on these quantities.
We present a novel method to detect the effects of dynamical friction in observed galaxy clusters. Following accretion into clusters, massive satellite galaxies will backsplash to systematically smaller radii than less massive satellites, an effect that may be detected by stacking the number density profiles of galaxies around clusters. We show that this effect may be understood using a simple toy model which reproduces the trends with halo properties observed in simulations. We search for this effect using SDSS redMaPPer clusters with richness 10<lambda<20, and find that bright (M_i<-21.5) satellites have smaller splashback radii than fainter (M_i>-20) satellites at 99% confidence.
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The most prodigious starburst galaxies are absent in massive galaxy clusters today, but their connection with large scale environments is less clear at $z\gtrsim2$. We present a search of large scale structure around a galaxy cluster core at $z=2.095$ using a set of spectroscopically confirmed galaxies. We find that both color-selected star-forming galaxies (SFGs) and dusty star-forming galaxies (DSFGs) show significant overdensities around the $z=2.095$ cluster. A total of 8 DSFGs (including 3 X-ray luminous active galactic nuclei, AGNs) and 34 SFGs are found within a 10 arcmin radius (corresponds to $\sim$15 cMpc at $z\sim2.1$) from the cluster center and within a redshift range of $\Delta z=0.02$, which leads to galaxy overdensities of $\delta_{\rm DSFG}\sim12.3$ and $\delta_{\rm SFG}\sim2.8$. The cluster core and the extended DSFG- and SFG-rich structure together demonstrate an active cluster formation phase, in which the cluster is accreting a significant amount of material from large scale structure while the more mature core may begin to virialize. Our finding of this DSFG-rich structure, along with a number of other protoclusters with excess DSFGs and AGNs found to date, suggest that the overdensities of these rare sources indeed trace significant mass overdensities. However, it remains puzzling how these intense star formers are triggered concurrently. Although an increased probability of galaxy interactions and/or enhanced gas supply can trigger the excess of DSFGs, our stacking analysis based on 850 $\mu$m images and morphological analysis based on rest-frame optical imaging do not show such enhancements of merger fraction and gas content in this structure.
We present a combined analysis of rest-frame far-UV (1000-2000 A) and rest-frame optical (3600-7000 A) composite spectra formed from very deep observations of a sample of 30 star-forming galaxies with z=2.4+/-0.1, selected to be representative of the full KBSS-MOSFIRE spectroscopic survey. Since the same massive stars are responsible for the observed FUV continuum and the excitation of the observed nebular emission, a self-consistent stellar population synthesis model must simultaneously match the details of the far-UV stellar+nebular continuum and-- when inserted as the excitation source in photoionization models-- account for all observed nebular emission line ratios. We find that only models including massive star binaries, having low stellar metallicity (Z_*/Z_{sun} ~ 0.1) but relatively high ionized gas-phase oxygen abundances (Z_{neb}/Z_{sun} ~ 0.5), can successfully match all of the observational constraints. We argue that this apparent discrepancy is naturally explained by highly super-solar O/Fe [4-5 times (O/Fe)_{sun}], expected for gas whose enrichment is dominated by the products of core-collapse supernovae. Once the correct ionizing spectrum is identified, photoionization models reproduce all of the observed strong emission line ratios, the direct T_e measurement of O/H, and allow accurate measurement of the gas-phase abundance ratios of N/O and C/O -- both of which are significantly sub-solar but, as for O/Fe, are in remarkable agreement with abundance patterns observed in Galactic thick disk, bulge, and halo stars with similar O/H. High nebular excitation is the rule at high-z (and rare at low-z) because of systematically shorter enrichment timescales (<<1 Gyr): low Fe/O environments produce harder (and longer-lived) stellar EUV spectra at a given O/H, enhanced by dramatic effects on the evolution of massive star binaries.
We present a physically clear cooling flow theory that explains the origin of warm diffuse gas seen primarily as highly ionized absorption line systems in the spectra of background sources. We predict the observed column densities of several highly ionized transitions such as O VI, O VII, Ne VIII, N V, and Mg X; and present a unified comparison of the model predictions with absorption lines seen in the Milky Way disk, Milky Way halo, starburst galaxies, the circumgalactic medium and the intergalactic medium at low and high redshifts. We show that diffuse gas seen in such diverse environments can be simultaneously explained by a simple model of radiatively cooling gas. We show that most of such absorption line systems are consistent with being collisionally ionized, and estimate the maximum likelihood temperature of the gas in each observation. This model satisfactorily explains why O VI is regularly observed around star-forming low-z L* galaxies, and why N V is rarely seen around the same galaxies. We predict that the typical O VI column densities seen around these galaxies would be an order of magnitude higher than the associated N V column densities. We further present some consequences of this model in quantifying the dynamics of the cooling gas around galaxies and predict the shock velocities associated with such flows. Useful formulae for both observers and simulators are presented.
We study the spatially resolved excitation properties of the ionised gas in a sample of 646 galaxies using integral field spectroscopy data from SDSS-IV MaNGA. Making use of Baldwin-Philips-Terlevich diagnostic diagrams we demonstrate the ubiquitous presence of extended (kpc scale) low ionisation emission-line regions (LIERs) in both star forming and quiescent galaxies. In star forming galaxies LIER emission can be associated with diffuse ionised gas, most evident as extra-planar emission in edge-on systems. In addition, we identify two main classes of galaxies displaying LIER emission: `central LIER' (cLIER) galaxies, where central LIER emission is spatially extended, but accompanied by star formation at larger galactocentric distances, and `extended LIER' (eLIER) galaxies, where LIER emission is extended throughout the whole galaxy. In eLIER and cLIER galaxies, LIER emission is associated with radially flat, low H$\alpha$ equivalent width of line emission ($<$ 3 \AA) and stellar population indices demonstrating the lack of young stellar populations, implying that line emission follows tightly the continuum due to the underlying old stellar population. The H$\alpha$ surface brightness radial profiles are always shallower than $\rm 1/r^{2}$ and the line ratio [OIII]$\lambda$5007/[OII]$\lambda$3727,29 (a tracer of the ionisation parameter of the gas) shows a flat gradient. This combined evidence strongly supports the scenario in which LIER emission is not due to a central point source but to diffuse stellar sources, the most likely candidates being hot, evolved (post-asymptotic giant branch) stars. Shocks are observed to play a significant role in the ionisation of the gas only in rare merging and interacting systems.
Extremely metal poor stars have been the focus of much recent attention owing to the expectation that their chemical abundances can shed light on the metal and dust yields of the earliest supernovae. We present our most realistic simulation to date of the astrophysical pathway to the first metal enriched stars. We simulate the radiative and supernova hydrodynamic feedback of a 60 Msun Population III star starting from cosmological initial conditions realizing Gaussian density fluctuations. We follow the gravitational hydrodynamics of the supernova remnant at high spatial resolution through its freely-expanding, adiabatic, and radiative phases, until gas, now metal-enriched, has resumed runaway gravitational collapse. Our findings are surprising: while the Population III progenitor exploded with a low energy of 10^51 erg and injected an ample metal mass of 6 Msun, the first cloud to collapse after the supernova explosion is a dense surviving primordial cloud on which the supernova blastwave deposited metals only superficially, in a thin, unresolved layer. The first metal-enriched stars can form at a very low metallicity, of only 2-5 x 10^-4 Zsun, and can inherit the parent cloud's highly elliptical, radially extended orbit in the dark matter gravitational potential.
We have detected molecular and atomic line emission from the hot and warm disks of two Class I sources, IRAS 03445+3242 and IRAS 04239+2436 using the high resolution Immersion GRating INfrared Spectrograph (IGRINS). CO overtone band transitions and near-IR lines of Na I and Ca I, all in emission, trace the hot inner disk while CO rovibrational absorption spectra of the first overtone transition trace the warm gas within the inner few AU of the disk. The emission-line profiles for both sources show evidence for Keplerian disks. A thin Keplerian disk with power-law temperature and column density profiles with a projected rotational velocity of $\sim$60--75 km s$^{-1}$ and a gas temperature of $\sim$3500 K at the innermost annulus can reproduce the CO overtone band emission. Na I and Ca I emission lines also arise from this disk, but they show complicated line features possibly affected by photospheric absorption lines. Multi-epoch observations show asymmetric variations of the line profiles on one-year (CO overtone bandhead and atomic lines for IRAS 03445+3242) or on one-day (atomic lines for IRAS 04239+2436) time scales, implying non-axisymmetric features in disks. The narrow CO rovibrational absorption spectra ($v$=0$\rightarrow$2) indicate that both warm ($>$ 150 K) and cold ($\sim$20--30 K) CO gas are present along the line of sight to the inner disk. This study demonstrates the power of IGRINS as a tool for studies of the sub-AU scale hot and AU-scale warm protoplanetary disks with its simultaneous coverage of the full H and K bands with high spectral resolution ($R$= 45,000) allowing many aspects of the sources to be investigated at once.
Emission lines from the broad emission line region (BELR) and the narrow emission line region (NELR) of active galactic nuclei (AGNs) are extensively studied. However, between these two regions emission lines are rarely detected. We present a detailed analysis of a quasar SDSS J232444.80-094600.3 (SDSS J2324$-$0946), which is remarkable for its strong intermediate-width emission lines (IELs) with FWHM $\approx$ 1800 \kmps. The IEL component is presented in different emission lines, including the permitted lines \lya\ $\lambda$1216, \civ\ $\lambda$1549, semiforbidden line \ciii\ $\lambda$1909, and forbidden lines \oiii\ $\lambda\lambda$4959, 5007. With the aid of photo-ionization models, we found that the IELs are produced by gas with a hydrogen density of $n_{\rm H} \sim 10^{6.2}-10^{6.3}~\rm cm^{-3}$, a distance to the central ionizing source of $R \sim 35-50$ pc, a covering factor of CF $\sim$ 6\%, and a dust-to-gas ratio of $\leq 4\%$ times of SMC. We suggest that the strong IELs of this quasar are produced by nearly dust-free and intermediate-density gas located at the skin of the dusty torus. Such strong IELs, served as a useful diagnose, can provide an avenue to study the properties of gas between the BELR and the NELR.
Using a Bayesian technology we derived distances and extinctions for over 100,000 red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey by taking into account spectroscopic constraints from the APOGEE stellar parameters and photometric constraints from 2MASS, as well as a prior knowledge on the Milky Way. Derived distances are compared with those from four other independent methods, the Hipparcos parallaxes, star clusters, APOGEE red clump stars, and asteroseismic distances from APOKASC (Rodrigues et al. 2014) and SAGA Catalogues (Casagrande et al. 2014). These comparisons covers four orders of magnitude in the distance scale from 0.02 kpc to 20 kpc. The results show that our distances agree very well with those from other methods: the mean relative difference between our Bayesian distances and those derived from other methods ranges from -4.2% to +3.6%, and the dispersion ranges from 15% to 25%. The extinctions toward all stars are also derived and compared with those from several other independent methods: the Rayleigh-Jeans Color Excess (RJCE) method, Gonzalez's two-dimensional extinction map, as well as three-dimensional extinction maps and models. The comparisons reveal that, overall, estimated extinctions agree very well, but RJCE tends to overestimate extinctions for cool stars and objects with low logg.
We have collected near-infrared to X-ray data of 20 multi-epoch heavily reddened SDSS quasars to investigate the physical mechanism of reddening. Of these, J2317+0005 is found to be a UV cutoff quasar. Its continuum, which usually appears normal, decreases by a factor 3.5 at 3000{\AA}, compared to its more typical bright state during an interval of 23 days. During this sudden continuum cut-off, the broad emission line fluxes do not change, perhaps due to the large size of the Broad Line Region (BLR), r > 23 / (1+z) days. The UV continuum may have suffered a dramatic drop out. However, there are some difficulties with this explanation. Another possibility is that the intrinsic continuum did not change, but was temporarily blocked out, at least towards our line of sight. As indicated by X-ray observations, the continuum rapidly recovers after 42 days. A comparison of the bright state and dim states would imply an eclipse by a dusty cloud with a reddening curve having a remarkably sharp rise shortward of 3500{\AA}. Under the assumption of being eclipsed by a Keplerian dusty cloud, we characterized the cloud size with our observations, however, which is a little smaller than the 3000\AA\ continuum-emitting size inferred from accretion disk models. Therefore, we speculate this is due to a rapid outflow or inflow with a dusty cloud passing through our line-of-sight to the center.
We present a Herschel/SPIRE survey of three protoclusters at z=2-3 (2QZCluster, HS1700, SSA22). Based on the SPIRE colours (S350/S250 and S500/S350) of 250 $\mu$m sources, we selected high redshift dusty star-forming galaxies potentially associated with the protoclusters. In the 2QZCluster field, we found a 4-sigma overdensity of six SPIRE sources around 4.5' (~2.2 Mpc) from a density peak of H$\alpha$ emitters at z=2.2. In the HS1700 field, we found a 5-sigma overdensity of eight SPIRE sources around 2.1' (~1.0 Mpc) from a density peak of LBGs at z=2.3. We did not find any significant overdensities in SSA22 field, but we found three 500 $\mu$m sources are concentrated 3' (~1.4 Mpc) east to the LAEs overdensity. If all the SPIRE sources in these three overdensities are associated with protoclusters, the inferred star-formation rate densities are 10$^3$-10$^4$ times higher than the average value at the same redshifts. This suggests that dusty star-formation activity could be very strongly enhanced in z~2-3 protoclusters. Further observations are needed to confirm the redshifts of the SPIRE sources and to investigate what processes enhance the dusty star-formation activity in z~2-3 protoclusters.
Aims. We aim to understand the high cyclic-to-linear $\rm C_3H_2$ ratio ($32 \pm 4$) observed toward L1544 by Spezzano et al. (2016). Methods. We combine a gas-grain chemical model with a physical model for L1544 to simulate the column densities of cyclic and linear $\rm C_3H_2$ observed toward L1544. The most important reactions for the formation and destruction of both forms of $\rm C_3H_2$ are identified, and their relative rate coefficients are varied to find the best match to the observations. Results. We find that the ratio of the rate coefficients of $\rm C_3H_3^+ + e^- \longrightarrow C_3H_2 + H$ for cyclic and linear $\rm C_3H_2$ must be $\sim 20$ in order to reproduce the observations, depending on the branching ratios assumed for the $\rm C_3H_3^+ + e^- \longrightarrow C_3H + H_2$ reaction. In current astrochemical networks it is assumed that cyclic and linear $\rm C_3H_2$ are formed in a 1:1 ratio in the aforementioned reactions. Laboratory studies and/or theoretical calculations are needed to confirm the results of our chemical modeling based on observational constraints.
The detection of quasars at $z>6$ unveils the presence of supermassive black holes (BHs) of a few billion solar masses. The rapid formation process of these extreme objects remains a fascinating and open issue. Such discovery implies that seed black holes must have formed early on, and grown via either rapid accretion or BH/galaxy mergers. In this theoretical review, we discuss in detail various BH seed formation mechanisms and the physical processes at play during their assembly. We discuss the three most popular BH formation scenarios, involving the (i) core-collapse of massive stars, (ii) dynamical evolution of dense nuclear star clusters, (iii) collapse of a protogalactic metal free gas cloud. This article aims at giving a broad introduction and an overview of the most advanced research in the field.
Herschel observations of nearby molecular clouds suggest that interstellar
filaments and prestellar cores represent two fundamental steps in the star
formation process. The observations support a picture of low-mass star
formation according to which ~ 0.1 pc-wide filaments form first in the cold
interstellar medium, probably as a result of large-scale compression of
interstellar matter by supersonic turbulent flows, and then prestellar cores
arise from gravitational fragmentation of the densest filaments. Whether this
scenario also applies to regions of high-mass star formation is an open
question, in part because Herschel data cannot resolve the inner width of
filaments in the nearest regions of massive star formation.
We used the bolometer camera ArTeMiS on the APEX telescope to map the central
part of the NGC6334 complex at a factor of > 3 higher resolution than Herschel
at 350 microns. Combining ArTeMiS data with Herschel data allowed us to study
the structure of the main filament of the complex with a resolution of 8" or <
0.07 pc at d ~ 1.7 kpc.
Our study confirms that this filament is a very dense, massive linear
structure with a line mass ranging from ~ 500 Msun/pc to ~ 2000 Msun/pc over
nearly 10 pc. It also demonstrates that its inner width remains as narrow as W
~ 0.15 +- 0.05 pc all along the filament length, within a factor of < 2 of the
characteristic 0.1 pc value found with Herschel for lower-mass filaments in the
Gould Belt. While it is not completely clear whether the NGC 6334 filament will
form massive stars or not in the future, it is two to three orders of magnitude
denser than the majority of filaments observed in Gould Belt clouds, and yet
has a very similar inner width. This points to a common physical mechanism for
setting the filament width and suggests that some important structural
properties of nearby clouds also hold in high-mass star forming regions.
Galactic systems, and the Universe at large, exhibit large dynamical anomalies: The observed matter in them falls very short of providing enough gravity to account for their dynamics. The mainstream response to this conundrum is to invoke large quantities of `dark matter' (DM) -- which purportedly supplies the needed extra gravity -- and also of `dark energy' (DE), to account for further anomalies in cosmology, such as the observed, accelerated expansion. The MOND paradigm offers a different solution: a breakdown of standard dynamics (gravity and/or inertia) in the limit of low accelerations -- below some acceleration $a_0$. In this limit, dynamics become space-time scale invariant, and is controlled by a gravitational constant $\mathcal{A}_0\equiv Ga_0$, which replaces Newton's $G$. With the new dynamics, the various detailed manifestations of the anomalies in galaxies disappear with no need for DM. The cosmological anomalies could, but need not have to do with small accelerations. For example, the need for DM in accounting for the expansion history of the Universe is eliminated if the relevant gravitational constant is $\approx 2\pi G$. Such a `renormalization' of $G$ could be a dimensionless parameter of a MOND theory. The constant $a_0$ turns out to carry cosmological connotations, in that $2\pi a_0\approx cH_0\approx c^2(\Lambda/3)^{1/2}$, where $H_0$ is the present expansion rate of the Universe, and $\Lambda$ the measured `cosmological constant'. There are MOND theories in which this `coincidence' is natural. I draw on enlightening historical and conceptual analogies from quantum theory to limelight aspects of MOND. I also explain how MOND may have strong connections with effects of the quantum vacuum on local dynamics.
The Seyfert galaxy NGC 985 is known to show a high-frequency excess in its radio continuum spectrum in a milli-Jansky level on the basis of previous observations at 1.4--15 GHz; a steep spectrum at low frequencies (a spectral index of $\alpha=-1.10 \pm 0.03$) changes at ~10 GHz into an inverted spectrum at higher frequencies ($\alpha=+0.86 \pm 0.09$). We conduct new observations at 15--43 GHz using the Very Large Array and at 100 GHz using the Nobeyama Millimeter Array. As a result, the high-frequency excess continuing at even higher radio frequencies up to 43 GHz has been confirmed. The non-detection at 100 GHz was not so strong constraint, and therefore the spectral behavior above 43 GHz remains unclear. The astrometric position of the high-frequency excess component coincides with the optical position of the Seyfert nucleus and the low-frequency radio position to an accuracy of 0.1 arcsec, corresponding to ~80 pc; the radio source size is constrained to be <0.02 arcsec, corresponding to <16 pc. We discuss the physical origin of the observed high-frequency excess component. Dust emission at the Rayleigh-Jeans regime, free--free emission from X-ray radiating high-temperature plasma, free--free emission from the ensemble of broad-line region clouds, or thermal synchrotron from hot accretion flow cannot be responsible for the observed radio flux. Compact jets under synchrotron self-absorption may be unlikely in terms of observed time scales. Alternatively, we cannot rule out the hypotheses of synchrotron jets free--free absorbed by a circumnuclear photo-ionized region, and self-absorbed nonthermal synchrotron from disk corona, as the origin of the high-frequency excess component.
Most radio galaxies are hosted by giant gas-poor ellipticals, but some contain significant amounts of dust, which is likely to be of external origin. In order to characterize the mid-IR properties of two of the most nearby and brightest merger-remnant radio galaxies of the Southern hemisphere, NGC 1316 (Fornax A) and NGC 612 (PKS 0131-36), we used observations with the Wide-field Infrared Survey Explorer (WISE) at wavelengths of 3.4, 4.6, 12 and 22 micron and Spitzer mid-infrared spectra. By applying a resolution-enhancement technique, new WISE images were produced at angular resolutions ranging from 2.6" to 5.5". Global measurements were performed in the four WISE bands, and stellar masses and star-formation rates were estimated using published scaling relations. Two methods were used to uncover the distribution of dust, one relying on two-dimensional fits to the 3.4 micron images to model the starlight, and the other one using a simple scaling and subtraction of the 3.4 micron images to estimate the stellar continuum contribution to the emission in the 12 and 22 micron bands. The two galaxies differ markedly in their mid-IR properties. The 3.4 micron brightness distribution can be well represented by the superposition of two Sersic models in NGC 1316 and by a Sersic model and an exponential disk in NGC 612. The WISE colors of NGC 1316 are typical of those of early-type galaxies; those of NGC 612 are in the range found for star-forming galaxies. From the 22 micron luminosity, we infer a star-formation rate of about 0.7 solar masses per year in NGC 1316 and about 7 solar masses per year in NGC 612. Spitzer spectroscopy shows that the 7.7-to-11.3 micron PAH line ratio is significantly lower in NGC 1316 than in NGC 612. The WISE images reveal resolved emission from dust in the central 1'-2' of the galaxies. (Abridged)
Star formation in molecular clouds can be triggered by the dynamical action of winds from massive stars. Furthermore, X-ray and UV fluxes from massive stars can influence the life time of surrounding circumstellar disks. We present the results of a 53 ks XMM-Newton observation centered on the Rho Ophiuchi A+B binary system. Rho Ophiiuchi lies in the center of a ring of dust, likely formed by the action of its winds. This region is different from the dense core of the cloud (L1688 Core F) where star formation is at work. X-rays are detected from Rho Ophiuchi as well as a group of surrounding X-ray sources. We detected 89 X-ray sources, 47 of them have at least one counterpart in 2MASS + All-WISE catalogs. Based on IR and X-ray properties, we can distinguish between young stellar objects (YSOs) belonging to the cloud and background objects. Among the cloud members, we detect 3 debris disk objects and 22 disk-less / Class III young stars. We show that these stars have ages in $5-10$ Myr, and are significantly older than the YSOs in L1688. We speculate that they are the result of an early burst of star formation in the cloud. An X-ray energy of $\ge5\times10^{44}$ ergs has been injected into the surrounding medium during the past $5$ Myr, we discuss the effects of such energy budget in relation to the cloud properties and dynamics.
The bibliographical compilation of stellar atmospheric parameters (Teff, logg, [Fe/H]) relying on high-resolution, high signal-to-noise spectroscopy started in the eighties with the so-called [Fe/H] catalogue, and was continued in 2010 with the PASTEL catalogue, which also includes determinations of Teff alone, based on various methods. Here we present an update of the PASTEL catalogue. The main journals and the CDS database have been surveyed to find relevant publications presenting new determinations of atmospheric parameters. As of February 2016, PASTEL includes 64082 determinations of either Teff or (Teff, logg, [Fe/H]) for 31401 stars, corresponding to 1142 bibliographical references. Some 11197 stars have a determination of the three parameters (Teff, logg, [Fe/H]) with a high-quality spectroscopic metallicity.
We present a weak-lensing and dynamical study of the complex cluster Abell 1758 (A1758, z = 0.278) supported by hydrodynamical simulations. This cluster is composed of two structures, each one experiencing a merger event. The Northern structure is composed of A1758NW & A1758NE, with lensing determined masses of 7.90_{-1.55}^{+1.89} x 10^{14} M_{\odot} and 5.49_{-1.33}^{+1.67} x 10^{14} M_{\odot}, respectively. They show a remarkable feature: while in A1758NW there is a spatial agreement among weak lensing mass distribution, intracluster medium and its brightest cluster galaxy (BCG) in A1758NE the X-ray peak is located 96_{-15}^{+14} arcsec away from the mass peak and BCG positions in a configuration we have called "demi-bullet". Give the detachment between gas and mass we could use the local surface mass density to estimate an upper limit for the dark matter self-interaction cross section: \sigma/m<5.83 cm^2 g^{-1}. Combining our velocity data with hydrodynamical simulations we have shown that A1758~NW & NE had their closest approach 0.27 Gyr ago and their merger axis is 21 +- 12 degrees from the plane of the sky. In the A1758S system we have measured a total mass of 4.96_{-1.19}^{+1.08} x 10^{14} M_{\odot} and, using radial velocity data, we found that the main merger axis is only 20 +- 4 degrees from the line-of-sight.
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Following the work of Cui et al. (2016b, hereafter Paper I), we investigate the dynamical state of the galaxy clusters from the theoretical point of view. After extending to vrial radius $R_{vir}$, we reselect out 123 clusters with $\log(M_{DM, vir}) \le 14.5$ from the galaxy cluster samples in Paper I, here DM indicate the dark-matter-only run. These clusters from the two hydro-dynamical runs are matched to the dark-matter-only run using the unique dark matter particle ID. We investigate 4 independent parameters, which are normally used to classify the cluster dynamical state. We find that the virial ratio $\eta$ from both hydro-dynamical runs is $\sim$ 10 per cent lower than from the dark-matter-only run; there is no clear bimodal distribution between the relaxed and un-relaxed clusters for all investigated parameters. Further, using the velocity dispersion deviation parameter $\zeta$ , which is defined as the ratio between cluster velocity dispersion $\sigma$ and the theoretical prediction $\sigma_t = \sqrt{G M_{total}/R}$, we find that there is a linear correlation between the virial ratio $\eta$ and the velocity dispersion deviation parameter $\zeta$. We propose to use this $\zeta$ parameter, which can be derived easily from observed clusters, as a substitute of the $\eta$ parameter to quantify the cluster dynamical state.
To understand the conditions under which dense, molecular gas is able to form within a galaxy, we post-process a series of three-dimensional galactic-disk-scale simulations with ray-tracing based radiative transfer and chemical network integration to compute the equilibrium chemical and thermal state of the gas. In performing these simulations we vary a number of parameters, such as the ISRF strength, vertical scale height of stellar sources, cosmic ray flux, to gauge the sensitivity of our results to these variations. Self-shielding permits significant molecular hydrogen (H2) abundances in dense filaments around the disk midplane, accounting for approximately ~10-15% of the total gas mass. Significant CO fractions only form in the densest, n>~10^3 cm^-3, gas where a combination of dust, H2, and self-shielding attenuate the FUV background. We additionally compare these ray-tracing based solutions to photochemistry with complementary models where photo-shielding is accounted for with locally computed prescriptions. With some exceptions, these local models for the radiative shielding length perform reasonably well at reproducing the distribution and amount of molecular gas as compared with a detailed, global ray tracing calculation. Specifically, an approach based on the Jeans Length with a T=40K temperature cap performs the best in regards to a number of different quantitative measures based on the H2 and CO abundances.
We explore the pitfalls which affect the comparison of the star-formation (SF) relation for nearby molecular clouds with that for distant compact molecular clumps. We show that both relations behave differently in the ($\Sigma_{gas}$, $\Sigma_{SFR}$) space, where $\Sigma_{gas}$ and $\Sigma_{SFR}$ are, respectively, the gas and SF rate surface densities, even when the physics of star formation is the same. This is because the SF relation of nearby clouds relates gas and star surface densities measured locally, that is, within a given interval of gas surface density, or at a given protostar location. We refer to such measurements as local measurements, and the corresponding SF relation as the local relation. In contrast, the stellar content of a distant molecular clump remains unresolved. Only the mean SF rate can be obtained from e.g. the clump infrared luminosity. One clump therefore provides one single point to the ($\Sigma_{gas}$, $\Sigma_{SFR}$) space, that is, its mean gas surface density and SF rate surface density. We refer to this SF relation as a global relation since it builds on the global properties of molecular clumps. Its definition therefore requires an ensemble of cluster-forming clumps. We show that, although the local and global relations have different slopes, this per se cannot be taken as evidence for a change in the physics of SF with gas surface density. It therefore appears that great caution should be taken when physically interpreting a composite SF relation, that is, a relation combining together local and global measurements.
Quiescent galaxies with little or no ongoing star formation dominate the galaxy population above $M_{*}\sim 2 \times 10^{10}~M_{\odot}$, where their numbers have increased by a factor of $\sim25$ since $z\sim2$. Once star formation is initially shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat subsequently accreted gas from stellar mass loss or mergers that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centers of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized gas velocity gradients from which we infer the presence of centrally-driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as $10\%$ of the population at $M_* \sim 2 \times 10^{10}~ M_{\odot}$. In a prototypical example, we calculate that the energy input from the galaxy's low-level active nucleus is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.
The space density distribution of galaxies in the absolute magnitude - rotation velocity plane: a volume-complete Tully-Fisher relation from CALIFA stellar kinematics
We present MUSE integral field spectroscopic data of the S0 galaxy NGC 3115 obtained during the instrument commissioning at the ESO Very Large Telescope (VLT). We analyse the galaxy stellar kinematics and stellar populations and present two dimensional maps of their associated quantities. We thus illustrate the capacity of MUSE to map extra-galactic sources to large radii in an efficient manner, i.e., ~4 Re, and provide relevant constraints on its mass assembly. We probe the well known set of substructures of NGC 3115 (its nuclear disc, stellar rings, outer kpc-scale stellar disc and spheroid) and show their individual associated signatures in the MUSE stellar kinematics and stellar populations maps. In particular, we confirm that NGC 3115 has a thin fast rotating stellar disc embedded in a fast rotating spheroid, and that these two structures show clear differences in their stellar age and metallicity properties. We emphasise an observed correlation between the radial stellar velocity, V, and the Gauss-Hermite moment, h3, creating a "butterfly" shape in the central 15" of the h3 map. We further detect the previously reported weak spiral and ring-like structures, and find evidence that these features can be associated with regions of younger mean stellar ages. We provide tentative evidence for the presence of a bar, despite the fact that the V-h3 correlation can be reproduced by a simple axisymmetric dynamical model. Finally, we present a reconstruction of the two dimensional star formation history of NGC 3115 and find that most of its current stellar mass was formed at early epochs (>12Gyr ago), while star formation continued in the outer (kpc-scale) stellar disc until recently. Since z~2, and within ~4 Re, we suggest that NGC 3115 has been mainly shaped by secular processes.
Polycyclic Aromatic Hydrocarbon (PAH) molecules have been long proposed to be
a major carrier of 'Unidentified Infrared' (UIR) emission bands that have been
observed ubiquitously in various astrophysical environments. These molecules
can potentially be an efficient reservoir of deuterium. Once the infrared
properties of the deuterium- containing PAHs are well understood both
experimentally and theoretically, the interstellar UIR bands can be used as a
valuable tool to infer the cause of the deuterium depletion in the ISM.
Density Functional Theory (DFT) calculations have been carried out on
deuterium-containing ovalene variants to study the infrared properties of these
molecules. These include deuterated ovalene, cationic deuterated ovalene,
deuteronated ovalene and deuterated-deuteronated ovalene. We present a D/H
ratio calculated from our theoretical study to compare with the observationally
proposed D/H ratio.
Average stellar orbits of the Galactic disk may have some small intrinsic ellipticity which breaks the exact axisymmetry and there may also be some migration of stars inwards or outwards. Both phenomena can be detected through kinematic analyses. We use the red clump stars selected spectroscopically from APOGEE (APO Galactic Evolution Experiment), with known distances and radial velocities, to measure the radial component of the Galactocentric velocities within 5 kpc$<R<$16 kpc, $|b|<5^\circ$ and within 20 degrees from the Sun-Galactic center line. The average Galactocentric radial velocity is $V_R=(1.48\pm 0.35)[R({\rm kpc})-(8.8\pm 2.7)]$ km/s outwards in the explored range, with a higher contribution from stars below the Galactic plane. Two possible explanations can be given for this result: i) the mean orbit of the disk stars is intrinsically elliptical with a Galactocentric radial gradient of eccentricity around 0.01 kpc$^{-1}$; or ii) there is a net secular expansion of the disk, in which stars within $R\approx 9-11$ kpc are migrating to the region $R\gtrsim 11$ kpc at the rate of $\sim 2$ M$_\odot $/yr, and stars with $R\lesssim 9$ kpc are falling toward the center of the Galaxy. This migration ratio would be unattainable for a long time and it should decelerate, otherwise the Galaxy would fade away in around 1 Gyr. At present, both hypotheses are speculative and one would need data on the Galactocentric radial velocities for other azimuths different to the center or anticenter in order to confirm one of the scenarios.
The galaxy cluster RXJ1257$+$4738 at $z=0.866$ is one of the highest redshift
clusters with a richness of multi-wavelength data, and thus a good target to
study the star formation-density relation at early epochs. Using a sample of
spectroscopically-confirmed cluster members, we derive the star formation rates
of our galaxies using two methods, (I) the relation between SFR and total
infrared luminosity extrapolated from the observed \textit{Spitzer} MIPS
24$\mu$m imaging data, and (II) spectral energy distribution (SED) fitting
using the MAGPHYS code, including eight different bands.
We show that, for this cluster, the SFR-density relation is very weak and
seems to be dominated by the two central galaxies and the SFR presents a mild
dependence on stellar mass, with more massive galaxies having higher SFR.
However, the specific SFR (SSFR) decreases with stellar mass, meaning that more
massive galaxies are forming less stars per unit of mass, and thus suggesting
that the increase in star-forming members is driven by cluster assembly and
infall.
If the environment is somehow driving the SF, one would expect a relation
between the SSFR and the cluster centric distance, but that is not the case. A
possible scenario to explain this lack of correlation is the contamination by
infalling galaxies in the inner part of the cluster which may be on their
initial pass through the cluster center. As these galaxies have higher SFRs for
their stellar mass, they enhance the mean SSFR in the center of the cluster.
We present radio continuum observations of the high-mass young stellar object (HMYSO) G345.4938+01.4677 made using the Australia Telescope Compact Array (ATCA) at 5, 9, 17, and 19 GHz. These observations provide definite evidence that the outer and inner pairs of radio lobes consist of shock ionized material being excited by an underlying collimated and fast protostellar jet emanating from a hypercompact HII region. By comparing with images taken 6 yr earlier at 5 and 9 GHz using the same telescope, we assess the proper motions of the radio sources. The outer West and East lobes exhibit proper motions of $64\pm12$ and $48\pm13$ milliarcsec yr$^{-1}$, indicating velocities projected in the plane of the sky and receding from G345.4938+01.4677 of $520$ and $390$ km s$^{-1}$, respectively. The internal radio lobes also display proper motion signals consistently receding from the HMYSO, with magnitudes of $17\pm11$ and $35\pm10$ milliarcsec yr$^{-1}$ for the inner West and East lobes, respectively. The morphology of the outer West lobe is that of a detached bow shock. At 17 and 19 GHz, the outer East lobe displays an arcuate morphology also suggesting a bow shock. These results show that disk accretion and jet acceleration --- possibly occurring in a very similar way compared with low-mass protostars --- is taking place in G345.4938+01.4677 despite the presence of ionizing radiation and the associated hypercompact HII region.
Despite intensive studies of protoplanetary disks, there is still no reliable way to determine their total mass and their surface density distribution, quantities that are crucial for describing both the structure and the evolution of disks up to the formation of planets. The goal of this work is to use less abundant CO isotopologues, whose detection is routine for ALMA, to infer the gas mass of disks. Isotope-selective effects need to be taken into account in the analysis, because they can significantly modify CO isotopologues line intensities. CO isotope-selective photodissociation has been implemented in the physical-chemical code DALI and 800 disk models have been run for a range of disk and stellar parameters. Dust and gas temperature structures have been computed self-consistently, together with a chemical calculation of the main species. Both disk structure and stellar parameters have been investigated. Total fluxes have been ray-traced for different CO isotopologues and for various transitions for different inclinations. A combination of 13CO and C18O total intensities allows inference of the total disk mass, although with non-negligible uncertainties. These can be overcome by employing spatially resolved observations, i.e. the disk's radial extent and inclination. Comparison with parametric models shows differences at the factor of a few level, especially for extremely low and high disk masses. Finally, total line intensities for different CO isotopologue and for various low-J transitions are provided and are fitted to simple formulae. The effects of a lower gas-phase carbon abundance and different gas/dust ratios are investigated as well, and comparison with other tracers is made. Disk masses can be determined within a factor of a few by comparing CO isotopologue lines observations with the simulated line fluxes, modulo the uncertainties in the volatile elemental abundances.
We present deep spectra of ring nebulae associated with Wolf-Rayet (WR) and O-type stars: NGC 6888, G2.4+1.4, RCW 58, S 308, NGC 7635 and RCW 52. The data have been taken with the 10m Gran Telescopio Canarias and the 6.5m Clay Telescope. We extract spectra of several apertures in some of the objects. We derive C$^{++}$ and O$^{++}$ abundances from faint recombination lines in NGC 6888 and NGC 7635, permitting to derive their C/H and C/O ratios and estimate the abundance discrepancy factor (ADF) of O$^{++}$. The ADFs are larger than the typical ones of normal HII regions but similar to those found in the ionised gas of star-forming dwarf galaxies. We find that chemical abundances are rather homogeneous in the nebulae where we have spectra of several apertures: NGC 6888, NGC 7635 and G2.4+1.4. We obtain very high values of electron temperature in a peripheral zone of NGC 6888, finding that shock excitation can reproduce its spectral properties. We find that all the objects associated with WR stars show N enrichment. Some of them also show He enrichment and O deficiency as well as a lower Ne/O than expected, this may indicate the strong action of the ON and NeNa cycles. We have compared the chemical composition of NGC 6888, G2.4+1.4, RCW 58 and S 308 with the nucleosynthesis predicted by stellar evolution models of massive stars. We find that non-rotational models of stars of initial masses between 25 and 40 solar masses seem to reproduce the observed abundance ratios of most of the nebulae.
We discuss 76 large amplitude transients (Delta-m>1.5) occurring in the nuclei of galaxies, nearly all with no previously known AGN. They have been discovered as part of the Pan-STARRS1 3pi survey, by comparison with SDSS photometry a decade earlier, and then monitored with the Liverpool Telescope. We also have optical spectroscopy for 51/76 of the objects. Based on colours, light curve shape, and spectra, these transients seem to fall into four groups. Some (~13%) turned out to be misclassified stars or objects of unknown type. Of the remainder, some (~21%$) are red/fast transients and are known or likely nuclear supernovae of various types. A few (~9%) are either radio sources or erratic variables and so likely blazars. However the majority (~66%) are blue and evolve slowly, on a timescale of years. Spectroscopy shows that these objects are AGN at z~ 0.3 - 1.4, which must have brightened since the SDSS photometry by around an order of magnitude. It is likely that most of these objects were in fact AGN a decade ago, but somewhat too weak to have been recognised as such by SDSS. These objects could then be classed as "hypervariable" AGN. In at least one case, the object has transitioned from a Type 1.9 to a Type 1 AGN. By searching the SDSS Stripe 82 quasar database, we find 15 comparison AGN which have changed over ~10 years by at least a factor 4, some of these seem to be blazars, but others are like the objects presented here, evolving smoothly over several years. We discuss several possible explanations for these slow blue hypervariables - (i) unusually luminous tidal disruption events, (ii) extinction events, (iii) changes in accretion state, and (iv) large amplitude microlensing by stars in foreground galaxies. A mixture of explanations (iii) and (iv) seems most likely. Both hold promise of considerable new insight into the AGN phenomenon.
We investigate the red supergiant (RSG) population of M31, obtaining radial velocities of 255 stars. These data substantiate membership of our photometrically-selected sample, demonstrating that Galactic foreground stars and extragalactic RSGs can be distinguished on the basis of B-V, V-R two-color diagrams. In addition, we use these spectra to measure effective temperatures and assign spectral types, deriving physical properties for 192 RSGs. Comparison with the solar-metallicity Geneva evolutionary tracks indicates astonishingly good agreement. The most luminous RSGs in M31 are likely evolved from 25-30 Mo stars, while the vast majority evolved from stars with initial masses of 20 Mo or less. There is an interesting bifurcation in the distribution of RSGs with effective temperatures that increases with higher luminosities, with one sequence consisting of early K-type supergiants, and with the other consisting of M-type supergiants that become later (cooler) with increasing luminosities. This separation is only partially reflected in the evolutionary tracks, although that might be due to the mis-match in metallicities between the solar Geneva models and the higher-than-solar metallicity of M31. As the luminosities increase the median spectral type also increases; i.e., the higher mass RSGs spend more time at cooler temperatures than do those of lower luminosities, a result which is new to this study. Finally we discuss what would be needed observationally to successfully build a luminosity function that could be used to constrain the mass-loss rates of RSGs as our Geneva colleagues have suggested.
We present a kinematic analysis of 152 low surface gravity M7-L8 dwarfs by adding 8 parallaxes, 38 radial velocities, and 19 proper motions. We find 39 objects to be high-likelihood or bona fide members of nearby moving groups, 92 objects to be ambiguous members and 21 objects that are non-members. We find that gravity classification and photometric color separate 5-150 Myr sources from > 3 Gyr field objects, but they do not correlate one-to-one with the narrower 5 -150 Myr age range. The absolute magnitudes of low-gravity sources from J band through W3 show a flux redistribution when compared to equivalent field sources that is correlated with spectral subtype. Clouds, which are a far more dominant opacity source for L dwarfs, are the likely cause. On CMDs, the latest-type low-gravity L dwarfs drive the elbow of the L/T transition up to 1 mag redder and 1 mag fainter than field dwarfs at M_J but are consistent with or brighter than the elbow at M_W1 and M_W2. Furthermore, there is an indication on CMD's (such as M_J versus (J-W2) of increasingly redder sequences separated by gravity classification. Examining bolometric luminosities for planets and low-gravity objects, we confirm that young M dwarfs are overluminous while young L dwarfs are normal compared to the field. This translates into warmer M dwarf temperatures compared to the field sequence while lower temperatures for L dwarfs.
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Combining the co-evolving chemistry, hydrodynamics and radiative transfer is an important step for star formation studies. It allows both a better link to observations and a self-consistent monitoring of the magnetic dissipation in the collapsing core. Our aim is to follow a chemo-dynamical evolution of collapsing dense cores with a reduced gas-grain chemical network. We present the results of radiative hydrodynamic (RHD) simulations of 1 M$_\odot$ isolated dense core collapse. The physical setup includes RHD and dynamical evolution of a chemical network. To perform those simulations, we merged the multi-dimensional adaptive-mesh-refinement code RAMSES and the thermo-chemistry Paris-Durham shock code. We simulate the formation of the first hydro-static core (FHSC) and the co-evolution of 56 species describing mainly H-C-O chemistry. Accurate benchmarking is performed, testing the reduced chemical network against a well-establiched complex network. We show that by using a compact set of reactions, one can match closely the CO abundances with results of a much more complex network. Our main results are: (a) We find that gas-grain chemistry post-processing can lead to one order of magnitude lower CO gas-phase abundances compared to the dynamical chemistry, with strongest effect during the isothermal phase of collapse. (b) The free-fall time has little effect on the chemical abundances for our choice of the parameters. (c) Dynamical chemical evolution is required to describe the CO gas phase abundance as well as the CO ice formation for the mean grain size larger then 1$\mu{}$m. (d) Furthermore, dust mean size and size distribution have a strong effect on chemical abundances and hence on the ionization degree and magnetic dissipation. We conclude that dust grain growth in the collapse simulations can be as important as coupling the collapse with chemistry.
Here we present the first results from ALMA observations of 1 mm polarized dust emission towards the W43-MM1 high mass star forming clump. We have detected a highly fragmented filament with source masses ranging from 14Msun to 312Msun, where the largest fragment, source A, is believed to be one of the most massive in our Galaxy. We found a smooth, ordered, and detailed polarization pattern throughout the filament which we used to derived magnetic field morphologies and strengths for 12 out of the 15 fragments detected ranging from 0.2 to 9 mG. The dynamical equilibrium of each fragment was evaluated finding that all the fragments are in a super-critical state which is consistent with previously detected infalling motions towards W43-MM1. Moreover, there are indications suggesting that the field is being dragged by gravity as the whole filament is collapsing.
We investigate Wolf-Rayet (WR) stars as a source of feedback contributing to the removal of natal material in the early evolution of massive star clusters. Despite previous work suggesting that massive star clusters clear out their natal material before the massive stars evolve into the WR phase, WR stars have been detected in several emerging massive star clusters. These detections suggest that the timescale for clusters to emerge can be at least as long as the time required to produce WR stars (a few million years), and could also indicate that WR stars may be providing the tipping point in the combined feedback processes that drive a massive star cluster to emerge. We explore the potential overlap between the emerging phase and the WR phase with an observational survey to search for WR stars in emerging massive star clusters hosting WR stars. We select candidate emerging massive star clusters from known radio continuum sources with thermal emission and obtain optical spectra with the 4m Mayall Telescope at Kitt Peak National Observatory and the 6.5m MMT. We identify 21 sources with significantly detected WR signatures, which we term "emerging WR clusters." WR features are detected in $\sim$50% of the radio-selected sample, and thus we find that WR stars are commonly present in massive star clusters currently emerging. The observed extinctions and ages suggest that clusters without WR detections remain embedded for longer periods of time, and may indicate that WR stars can aid, and therefore accelerate, the emergence process.
We present Adaptive Optics assisted near-IR integral field spectroscopic observations of a luminous quasar at $z = 2.4$, previously observed as the first known example at high redshift of large scale quasar-driven outflow quenching star formation in its host galaxy. The nuclear spectrum shows broad and blueshifted H$\beta$ in absorption, which is tracing outflowing gas with high densities ($>10^8$ - $10^9$ cm$^{-3}$) and velocities in excess of 10,000 km s$^{-1}$. The properties of the outflowing clouds (covering factor, density, column density and inferred location) indicate that they likely originate from the Broad Line Region. The energetics of such nuclear regions are consistent with that observed in the large scale outflow, supporting models in which quasar driven outflows originate from the nuclear region and are energy conserving. We note that the asymmetric profile of both the H$\beta$ and H$\alpha$ emission lines is likely due to absorption by the dense outflowing gas along the line of sight. This outflow-induced asymmetry has implications on the estimation of the black hole mass using virial estimators, and warns about such effects for several other quasars characterized by similar line asymmetries. More generally, our findings may suggest a broader revision of the decomposition and interpretation of quasar spectral features, in order to take into account the presence of potential broad blueshifted Balmer absorption lines. Our high spatial resolution data also reveals redshifted, dynamically colder nebular emission lines, likely tracing an inflowing stream.
From 2013 April to 2014 April, we performed an X-ray and optical simultaneous monitoring of the type 1.5 Seyfert galaxy NGC 3516. It employed Suzaku, and 5 Japanese ground-based telescopes, the Pirka, Kiso Schmidt, Nayuta, MITSuME, and the Kanata telescopes. The Suzaku observations were conducted seven times with various intervals ranging from days, weeks, to months, with an exposure of $\sim50$ ksec each. The optical $B$-band observations not only covered those of Suzaku almost simultaneously, but also followed the source as frequently as possible. As a result, NGC 3516 was found in its faint phase with the 2-10 keV flux of $0.21-2.70 \times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$. The 2-45 keV X-ray spectra were composed of a dominant variable hard power-law continuum with a photon index of $\sim1.7$, and a non-relativistic reflection component with a prominent Fe-K$\alpha$ emission line. Producing the $B$-band light curve by differential image photometry, we found that the $B$-band flux changed by $\sim2.7 \times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$, which is comparable to the X-ray variation, and detected a significant flux correlation between the hard power-law component in X-rays and the $B$-band radiation, for the first time in NGC 3516. By examining their correlation, we found that the X-ray flux preceded that of $B$ band by $2.0^{+0.7}_{-0.6}$ days ($1\sigma$ error). Although this result supports the X-ray reprocessing model, the derived lag is too large to be explained by the standard view which assumes a "lamppost"-type X-ray illuminator located near a standard accretion disk. Our results are better explained by assuming a hot accretion flow and a truncated disk.
We implement novel numerical models of AGN feedback in the SPH code GADGET-3, where the energy from a supermassive black hole (BH) is coupled to the surrounding gas in the kinetic form. Gas particles lying inside a bi-conical volume around the BH are imparted a one-time velocity (10,000 km/s) increment. We perform hydrodynamical simulations of isolated cluster (total mass 10^14 /h M_sun), which is initially evolved to form a dense cool core, having central T<10^6 K. A BH resides at the cluster center, and ejects energy. The feedback-driven fast wind undergoes shock with the slower-moving gas, which causes the imparted kinetic energy to be thermalized. Bipolar bubble-like outflows form propagating radially outward to a distance of a few 100 kpc. The radial profiles of median gas properties are influenced by BH feedback in the inner regions (r<20-50 kpc). BH kinetic feedback, with a large value of the feedback efficiency, depletes the inner cool gas and reduces the hot gas content, such that the initial cool core of the cluster is heated up within a time 1.9 Gyr, whereby the core median temperature rises to above 10^7 K, and the central entropy flattens. Our implementation of BH thermal feedback (using the same efficiency as kinetic), within the star-formation model, cannot do this heating, where the cool core remains. The inclusion of cold gas accretion in the simulations produces naturally a duty cycle of the AGN with a periodicity of 100 Myr.
Using Hubble data, including new grism spectra, Oesch et al. (2016) recently identified GN-z11, a $M_\textrm{UV}$=-21.1 galaxy at $z$=11.1 (just 400 Myr after the Big Bang). With an estimated stellar mass of $\sim$10$^9$M$_\odot$, this galaxy is surprisingly bright and massive, raising questions as to how such an extreme object could form so early in the Universe. Using Meraxes, a semi-analytic galaxy formation model developed as part of the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulations (DRAGONS) programme, we investigate the potential formation mechanisms and eventual fate of GN-z11. The volume of our simulation is comparable to that of the discovery observations and possesses two analogue galaxies of similar luminosity to this remarkably bright system. Existing in the two most massive subhaloes at $z$=11.1 ($M_\textrm{vir}$=1.4$\times 10^{11}$M$_\odot$ and 6.7$\times 10^{10}$M$_\odot$), our model analogues show excellent agreement with all available observationally derived properties of GN-z11. Although they are relatively rare outliers from the full galaxy population at high-$z$, they are no longer the most massive or brightest systems by $z$=5. Furthermore, we find that both objects possess relatively smooth, but extremely rapid mass growth histories with consistently high star formation rates and UV luminosities at $z{>}11$, indicating that their brightness is not a transient, merger driven feature. Our model results suggest that future wide-field surveys with JWST may be able to detect the progenitors of GN-z11 analogues out to $z{\sim}$13-14, pushing the frontiers of galaxy-formation observations to the early phases of cosmic reionization and providing a valuable glimpse of the first galaxies to reionize the Universe on large scales.
We use the coadded spectra of 32 epochs of Sloan Digital Sky Survey (SDSS) Reverberation Mapping Project observations of 482 quasars with z>1.46 to highlight systematic biases in the SDSS- and BOSS-pipeline redshifts due to the natural diversity of quasar properties. We investigate the characteristics of this bias by comparing the BOSS-pipeline redshifts to an estimate from the centroid of HeII 1640. HeII has a low equivalent width but is often well-defined in high-S/N spectra, does not suffer from self-absorption, and has a narrow component that, when present (the case for about half of our sources), produces a redshift estimate that, on average, is consistent with that determined from [OII] to within 1-sigma of the quadrature sum of the HeII and [OII] centroid measurement uncertainties. The large redshift differences of ~1000 km/s, on average, between the BOSS-pipeline and HeII-centroid redshifts suggest there are significant biases in a portion of BOSS quasar redshift measurements. Adopting the HeII-based redshifts shows that CIV does not exhibit a ubiquitous blueshift for all quasars, given the precision probed by our measurements. Instead, we find a distribution of CIV centroid blueshifts across our sample, with a dynamic range that (i) is wider than that previously reported for this line, and (ii) spans CIV centroids from those consistent with the systemic redshift to those with significant blueshifts of thousands of kilometers per second. These results have significant implications for measurement and use of high-redshift quasar properties and redshifts and studies based thereon.
Current theories assume that the low intensity of the stellar extragalactic background light (stellar EBL) is caused primarily by finite age of the Universe because the finite age limits the number of photons pumped into the space by galaxies and thus the sky is dark in the night. We oppose this opinion and show that two main factors are responsible for the extremely low intensity of the observed stellar EBL: (1) a low mean surface brightness of galaxies, which causes a low luminosity density in the local Universe, and (2) light extinction due to absorption by galactic and intergalactic dust. Dust produces a partial opacity of galaxies and of the Universe. The galactic opacity reduces the intensity of light from more distant background galaxies obscured by foreground galaxies. The effective extinction AV for light passing through a galaxy is 0.2 mag. This causes that distant background galaxies do not contribute to the EBL significantly. In addition, light of distant galaxies is dimmed due to absorption by intergalactic dust. Even a minute intergalactic opacity of 1x10^(-2) mag per Gpc is high enough to produce significant effects on the EBL. The absorbed starlight heats up the galactic and intergalactic dust and is further re-radiated at the IR, FIR and micro-wave spectrum. Assuming static infinite universe with no galactic and intergalactic dust, the stellar EBL should be as high as the surface brightness of stars. However, if dust is considered, the predicted stellar EBL is about 290 nWm^(-2)sr^(-1), which is only 5 times higher than the observed value. Hence, the presence of dust has higher impact on the EBL than currently assumed. In the expanding universe, the calculated value of the EBL is further decreased, because the obscuration effect and intergalactic absorption become more pronounced at high redshifts when the matter was concentrated at smaller volume than at present.
HH 111 is a Class I protostellar system at a distance of ~ 400 pc, with the central source VLA 1 associated with a rotating disk deeply embedded in a flattened envelope. Here we present the observations of this system at ~ 0.6" (240 AU) resolution in C18O (J=2-1) and 230 GHz continuum obtained with Atacama Large Millimeter/Submillimeter Array, and in SO obtained with Submillimeter Array. The observations show for the first time how a Keplerian rotating disk can be formed inside a flattened envelope. The flattened envelope is detected in C18O, extending out to >~ 2400 AU from the VLA 1 source. It has a differential rotation, with the outer part (>~ 2000 AU) better described by a rotation that has constant specific angular momentum and the innermost part (<~ 160 AU) by a Keplerian rotation. The rotationally supported disk is therefore relatively compact in this system, which is consistent with the dust continuum observations. Most interestingly, if the flow is in steady state, there is a substantial drop in specific angular momentum in the envelope-disk transition region from 2000 AU to 160 AU, by a factor of ~ 3. Such a decrease is not expected outside a disk formed from simple hydrodynamic core collapse, but can happen naturally if the core is significantly magnetized, because magnetic fields can be trapped in the transition region outside the disk by the ram pressure of the protostellar accretion flow, which can lead to efficient magnetic braking. In addition, SO shock emission is detected around the outer radius of the disk and could trace an accretion shock around the disk.
We present the properties of X-ray detected dust obscured galaxies (DOGs) in the Chandra Deep Field South. In recent years, it has been proposed that a significant percentage of the elusive Compton-thick (CT) active galactic nuclei (AGN) could be hidden among DOGs. In a previous work, we presented the properties of X-ray detected DOGs by making use of the deepest X-ray observations available at that time, the 2Ms observations of the Chandra deep fields. In that work, we only found a moderate percentage ($<$ 50%) of CT AGN among the DOGs sample, but we were limited by poor photon statistics. In this paper, we use not only a deeper 6 Ms Chandra survey of the Chandra Deep Field South (CDF-S), but combine these data with the 3 Ms XMM-Newton survey of the CDF-S. We also take advantage of the great coverage of the CDF-S region from the UV to the far-IR to fit the spectral energy distributions (SEDs) of our sources. Out of the 14 AGN composing our sample, 9 are highly absorbed (but only 3 could be CT AGN), whereas 2 look unabsorbed, and the other 3 are only moderately absorbed. In only one of the CT AGN, we detect a strong Fe K$\alpha$ emission line; the source is already classified as a CT AGN with Chandra data in a previous work. For the other two CT candidates, the non-detection of the line could be because of the low number of counts in their X-ray spectra, but their location in the L$_{\rm 2-10\,keV}$/L$_{12\mu m}$ plot supports their CT classification. Although a higher number of CT sources could be hidden among the X-ray undetected DOGs, our results indicate that DOGs could be as well composed of only a fraction of CT AGN plus a number of moderate to highly absorbed AGN, as previously suggested. From our study of the X-ray undetected DOGs in the CDF-S, we estimate a percentage between 13 and 44% of CT AGN among the whole population of DOGs.
In the previous papers in this series, we have measured the stellar and \hi content in a sample of edge-on galaxies. In the present paper, we perform a simultaneous rotation curve and vertical force field gradient decomposition for five of these edge-on galaxies. The rotation curve decomposition provides a measure of the radial dark matter potential, while the vertical force field gradient provide a measure of the vertical dark matter potential. We fit dark matter halo models to these potentials. Using our \hi self-absorption results, we find that a typical dark matter halo has a less dense core ($0.094\pm0.230$\,M$_\odot$/pc$^3$) compared to an optically thin \hi model ($0.150\pm0.124$\,M$_\odot$/pc$^3$). The HI self-absorption dark matter halo has a longer scale length $R_c$ of $1.42\pm 3.48$\,kpc, versus $1.10\pm 1.81$\,kpc for the optically thin HI model. The median halo shape is spherical, at $q=1.0\pm0.6$ (self-absorbing \hi), while it is prolate at $q=1.5\pm0.6$ for the optically thin. Our best results were obtained for ESO\,274-G001 and UGC\,7321, for which we were able to measure the velocity dispersion in Paper III. These two galaxies have drastically different halo shapes, with one oblate and one strongly prolate. Overall, we find that the many assumptions required make this type of analysis susceptible to errors.
The L1544 prestellar core has been observed as part of the ASAI IRAM Large Program at 3 mm. These observations led to the detection of many complex molecules. In this Letter, we report the detection of two lines, at 85.5 GHz (4,0,4-3,0,3) and 106.9 GHz (5,0,5-4,0,4), respectively, of the protonated carbon dioxide ion, HOCO+. We also report the tentative detection of the line at 100.4 GHz (5,0,5-4,0,4) of DOCO+. The non-LTE analysis of the detected lines shows that the HOCO+ emission originates in the external layer where non-thermal desorption of other species has previously been observed. Its abundance is (5 +/- 2) e-11. Modelling of the chemistry involved in the formation and destruction of HOCO+ provides a gaseous CO2 abundance of 2e-7 (with respect to H2) with an upper limit of 2e-6.
We have developed a computationally competitive N-body model of a previrialized aggregation of galaxies in a flat LambdaCDM universe to assess the role of the multiple mergers that take place during the formation stage of such systems in the configuration of the remnants assembled at their centres. An analysis of a suite of 48 simulations of low-mass forming groups (of about 1E13 solar masses) demonstrates that the gravitational dynamics involved in their hierarchical collapse is capable of creating realistic first-ranked galaxies without the aid of dissipative processes. Our simulations indicate that the brightest group galaxies (BGGs) constitute a distinct population from other group members, sketching a scenario in which the assembly path of these objects is dictated largely by the formation of their host system. We detect significant differences in the distribution of Sersic indices and total magnitudes, as well as a luminosity gap between BGGs and the next brightest galaxy that is positively correlated with the total luminosity of the parent group. Such gaps arise from both the grow of BGGs at the expense of lesser companions and the decrease in the relevance of second-ranked objects in equal measure. This results in a dearth of intermediate-mass galaxies which explains the characteristic central dip detected in their luminosity functions in dynamically young galaxy aggregations. The fact that the basic global properties of our BGGs define a thin mass fundamental plane strikingly similar to that followed giant early-type galaxies in the local universe reinforces confidence in the results obtained.
Observational evidence indicates that the role of gas is secondary to that of gravity in the formation of the most luminous spheroids inhabiting the centres of galaxy associations, as originally conjectured in the late 80's/early 90's. However, attempts to explain the origin of the Fundamental Plane (FP) of massive early-type galaxies (ETGs) -- a tilted version of the scaling relation connecting the size, velocity dispersion and mass of virialized homologous systems -- based on sequences of pairwise mergers, have systematically concluded that dissipation cannot be ignored. We use controlled simulations of the previrialization stage of galaxy groups to show that multiple collisionless merging is capable of creating realistic first-ranked galaxies. Our mock remnants define a thin FP that perfectly fits data from all kinds of giant ETGs in the local volume, showing the existence of a unified relationship for these systems. High-ranked galaxies occupy in the FP different areas than standard objects, a segregation which is viewed essentially as zero-point offsets in the 2D correlations arising from standard projections of this plane. Our findings make a strong case for considering hierarchical dissipationless merging a viable route for the formation of the largest galaxies in the universe.
Diffuse Galactic light (DGL) has been observed in the optical since the 1930s. We propose that, when observed in the optical with deep imaging surveys, it can be used as a tracer of the turbulent cascade in the diffuse interstellar medium, down to scales of about 1 arcsec. Here we present a power spectrum analysis of the dust column density of a diffuse cirrus at high Galactic latitude (l ~ 198 deg, b ~ 32 deg) as derived from the combination of a MegaCam g-band image, obtained as part of the MATLAS Large Programme at the CFHT, with Planck Radiance and Wise 12 micron data. The combination of these three datasets allowed us to compute the density power spectrum of the HI over more than three orders of magnitudes in scales. We found that the density field is well described by a single power law over scales ranging from 0.01 to 50 pc. The exponent of the power spectrum, gamma=-2.9 +- 0.1, is compatible with what is expected for thermally bi-stable and turbulent HI. We did not find any steepening of the power spectrum at small scales indicating that the typical scale at which turbulent energy is dissipated in this medium is smaller than 0.01pc. The ambipolar diffusion scenario that is usually proposed as the main dissipative agent, is consistent with our data only if the density of the cloud observed is higher than the typical values assumed for the Cold Neutral Medium (CNM) gas. We discuss the new avenue offered by deep optical imaging surveys for the study of the low density ISM structure and turbulence.
We present near-IR images of five luminous quasars at z~2 and one at z~4 obtained with an experimental adaptive optics instrument at the ESO Very Large Telescope. The observations are part of a program aimed at demonstrating the capabilities of multi-conjugated adaptive optics imaging combined with the use of natural guide stars for high spatial resolution studies on large telescopes. The observations were mostly obtained under poor seeing conditions but in two cases. In spite of these non optimal conditions, the resulting images of point sources have cores of FWHM ~0.2 arcsec. We are able to characterize the host galaxy properties for 2 sources and set stringent upper limits to the galaxy luminosity for the others. We also report on the expected capabilities for investigating the host galaxies of distant quasars with adaptive optics systems coupled with future Extremely Large Telescopes. Detailed simulations show that it will be possible to characterize compact (2-3 kpc) quasar host galaxies for QSOs at z = 2 with nucleus K-magnitude spanning from 15 to 20 (corresponding to absolute magnitude -31 to -26) and host galaxies that are 4 mag fainter than their nuclei.
We used models of thermally-pulsing asymptotic giant branch (AGB) stars, that also describe the dust-formation process in the wind, to interpret the combination of near- and mid-infrared photometric data of the dwarf galaxy IC 1613. This is the first time that this approach is extended to an environment different from the Milky Way and the Magellanic Clouds (MCs). Our analysis, based on synthetic population techniques, shows a nice agreement between the observations and the expected distribution of stars in the colour-magnitude diagrams obtained with JHK and Spitzer bands. This allows a characterization of the individual stars in the AGB sample in terms of mass, chemical composition, and formation epoch of the progenitors. We identify the stars exhibiting the largest degree of obscuration as carbon stars evolving through the final AGB phases, descending from 1-1.25Msun objects of metallicity Z=0.001 and from 1.5-2.5Msun stars with Z=0.002. Oxygen-rich stars constitute the majority of the sample (65%), mainly low mass stars (<2Msun) that produce a negligible amount of dust (<10^{-7}Msun/yr). We predict the overall dust-production rate from IC 1613, mostly determined by carbon stars, to be 6x10^{-7}Msun/yr with an uncertainty of 30%. The capability of the current generation of models to interpret the AGB population in an environment different from the MCs opens the possibility to extend this kind of analysis to other Local Group galaxies.
We select from Paper I a sample of 306 massive star clusters observed with the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) in the vicinity fields of M31 and M33 and determine their metallicities, ages and masses. Metallicities and ages are estimated by fitting the observed integrated spectra with stellar synthesis population (SSP) models with a pixel-to-pixel spectral fitting technique. Ages for most young clusters are also derived by fitting the multi-band photometric measurements with model spectral energy distributions (SEDs). The estimated cluster ages span a wide range, from several million years to the age of the universe. The numbers of clusters younger and older than 1 Gyr are respectively 46 and 260. With ages and metallicities determined, cluster masses are then estimated by comparing the multi-band photometric measurements with SSP model SEDs. The derived masses range from $\sim 10^{3}$ to $\sim 10^7$ $M_{\odot}$, peaking at $\sim 10^{4.3}$ and $\sim 10^{5.7}$ $M_{\odot}$ for young ($< 1$ Gyr) and old ($>1$ Gyr) clusters, respectively. Our estimated metallicities, ages and masses are in good agreement with available literature values. Old clusters richer than [Fe/H] $\sim -0.7$ dex have a wide range of ages. Those poorer than [Fe/H] $\sim -0.7$ dex seem to be composed of two groups, as previously found for Galactic GCs -- one of the oldest ages with all values of metallicity down to $\sim -2$ dex and another with metallicity increasing with decreasing age. The old clusters in the inner disk of M\,31 (0 -- 30 kpc) show a clear metallicity gradient measured at $-0.038\pm0.023$ dex/kpc.
We have entered an era of large spectroscopic surveys in which we can measure, through automated pipelines, the atmospheric parameters and chemical abundances for large numbers of stars. Calibrating these survey pipelines using a set of "benchmark stars" in order to evaluate the accuracy and precision of the provided parameters and abundances is of utmost importance. The recent proposed set of Gaia FGK benchmark stars of Heiter et al. (2015) has no recommended stars within the critical metallicity range of $-2.0 <$ [Fe/H] $< -1.0$ dex. In this paper, we aim to add candidate Gaia benchmark stars inside of this metal-poor gap. We began with a sample of 21 metal-poor stars which was reduced to 10 stars by requiring accurate photometry and parallaxes, and high-resolution archival spectra. The procedure used to determine the stellar parameters was similar to Heiter et al. (2015) and Jofre et al. (2014) for consistency. The effective temperature (T$_{\mathrm{eff}}$) of all candidate stars was determined using the Infrared Flux Method utilizing multi-band photometry. The surface gravity (log g) was determined through fitting stellar evolutionary tracks. The [Fe/H] was determined using four different spectroscopic methods fixing the T$_{\mathrm{eff}}$ and log g from the values determined independent of spectroscopy. We discuss, star-by-star, the quality of each parameter including how it compares to literature, how it compares to a spectroscopic run where all parameters are free, and whether Fe I ionisation-excitation balance is achieved. From the 10 stars, we recommend a sample of five new metal-poor benchmark candidate stars which have consistent T$_{\mathrm{eff}}$ , log g, and [Fe/H] determined through several means. These stars can be used for calibration and validation purpose of stellar parameter and abundance pipelines and should be of highest priority for future interferometric studies.
Inferring cosmological parameters from time-delay strong lenses requires a significant investment of telescope time; it is therefore tempting to focus on the systems with the brightest sources, the highest image multiplicities and the widest image separations. We investigate if this selection bias can influence the properties of the lenses studied and the cosmological parameters that are inferred. Using a population of lenses with ellipsoidal powerlaw density profiles, we build a sample of double and quadruple image systems. Assuming reasonable thresholds on image separation and flux, based on current lens monitoring campaigns, we find that the typical density profile slopes of monitorable lenses are significantly shallower than the input ensemble. From a sample of quadruple image lenses we find that this selection function can introduce a 3.5% bias on the inferred time-delay distances if the ensemble of deflector properties is used as a prior for a cosmographical analysis. This bias remains at the 2.4% level when high resolution imaging of the quasar host is used to precisely infer the density profiles of individual lenses. We also investigate if the lines-of-sight for monitorable strong lenses are biased. After adding external convergence, $\kappa$, and shear to our lens population we find that the expectation value for $\kappa$ is increased by 0.004 and 0.009 for doubles and quads respectively. $\kappa$ is degenerate with the value of $H_0$ inferred from time delays; fortunately the shift in $\kappa$ only induces a 0.9 (0.4) percent bias on $H_0$ for quads (doubles). We therefore conclude that whilst the properties of typical quasar lenses and their lines-of-sight do deviate from the global population, the total magnitude of this effect is likely a subdominant effect for current analyses, but has the potential to be a major systematic for samples of $\sim$25 or more lenses.
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