We present results on the variation of Polycyclic Aromatic Hydrocarbon (PAH) emission at 7.7 micron in galaxies spanning a wide range in metallicity at z~2. For this analysis, we use rest-frame optical spectra of 476 galaxies at 1.37$\leq z\leq$2.61 from the MOSFIRE Deep Evolution Field (MOSDEF) survey to infer metallicities and ionization states. Spitzer/MIPS 24 micron observations are used to derive rest-frame 7.7 micron luminosities (L(7.7)) and far-IR data from Herschel/PACS 100 and 160 micron to measure total IR luminosities (L(IR)). We find significant trends between the ratio of L(7.7) to L(IR) (and to dust-corrected SFR) and both metallicity and [OIII]/[OII] (O$_{32}$) emission-line ratio. The latter is an empirical proxy for the ionization parameter. These trends indicate a paucity of PAH molecules in low metallicity environments with harder and more intense radiation fields. Additionally, L(7.7)/L(IR) is significantly lower in the youngest quartile in our sample (ages of ~ 400 Myr) compared to older galaxies, which may be a result of the delayed production of PAHs by AGB stars. The relative strength of L(7.7) to L(IR) is also lower by a factor of ~2 for galaxies with masses M$_*<10^{10} M_{\odot}$, compared to the more massive ones. We demonstrate that commonly-used conversions of L(7.7) (or 24 micron flux density; f(24)) to L(IR) underestimate the IR luminosity by more than a factor of 2 at M$_*$~$10^{9.6-10.0} M_{\odot}$. Consequently, the SFR-M$_*$ relation has a shallower slope than previously derived from studies that neglected the metallicity dependence of the 24 micron-to-IR conversion factor. Our results suggest a higher IR luminosity density at z~2 than previously measured, which corresponds to a ~ 30% increase in the SFR density.
We characterize the column density probability distributions functions (PDFs) of the atomic hydrogen gas, HI, associated with seven Galactic molecular clouds (MCs). We use 21 cm observations from the Leiden/Argentine/Bonn Galactic HI Survey to derive column density maps and PDFs. We find that the peaks of the HI PDFs occur at column densities ranging from ~1-2$\times 10^{21}$ cm$^2$ (equivalently, ~0.5-1 mag). The PDFs are uniformly narrow, with a mean dispersion of $\sigma_{HI}\approx 10^{20}$ cm$^2$ (~0.1 mag). We also investigate the HI-to-H$_2$ transition towards the cloud complexes and estimate HI surface densities ranging from 7-16 $M_\odot$ pc$^{-2}$ at the transition. We propose that the HI PDF is a fitting tool for identifying the HI-to-H$_2$ transition column in Galactic MCs.
We investigate the integrated far-ultraviolet (FUV) emission from globular clusters. We present new FUV photometry of M~87's clusters based on archival HST WFPC2 F170W observations. We use these data to test the reliability of published photometry based on HST STIS FUV-MAMA observations, which are now known to suffer from significant red-leak. We generally confirm these previous FUV detections, but suggest they may be somewhat fainter. We compare the FUV emission from bright ($M_{V} < -9.0$) clusters in the Milky Way, M~31, M~81 and M~87 to each other and to the predictions from stellar populations models. Metal-rich globular clusters show a large spread in FUV-V, with some clusters in M~31, M~81 and M~87 being much bluer than standard predictions. This requires that some metal-rich clusters host a significant population of blue/extreme horizontal branch (HB) stars. These hot HB stars are not traditionally expected in metal-rich environments, but are a natural consequence of multiple populations in clusters - since the enriched population is observed to be He-enhanced and will therefore produce bluer HB stars, even at high metallicity. We conclude that the observed FUV emission from metal-rich clusters in M~31, M~81 and M~87 provides evidence that He-enhanced second populations, similar to those observed directly in the Milky Way, may be a ubiquitous feature of globular clusters in the local universe. Future HST FUV photometry is required to both confirm our interpretation of these archival data and provide constraints on He-enriched second populations of stars in extra-galactic globular clusters.
Standard galaxy formation models predict that large-scale double-lobed radio sources, known as DRAGNs, will always be hosted by elliptical galaxies. In spite of this, in recent years a small number of spiral galaxies have also been found to host such sources. These so-called spiral DRAGNs are still extremely rare, with only $\sim 5$ cases being widely accepted. Here we report on the serendipitous discovery of a new spiral DRAGN in data from the Giant Metrewave Radio Telescope (GMRT) at 322 MHz. The host galaxy, MCG+07-47-10, is a face-on late-type Sbc galaxy with distinctive spiral arms and prominent bulge suggesting a high black hole mass. Using WISE infra-red and GALEX UV data we show that this galaxy has a star formation rate of 0.16-0.75 M$_{\odot}$yr$^{-1}$, and that the radio luminosity is dominated by star-formation. We demonstrate that this spiral DRAGN has similar environmental properties to others of this class, but has a comparatively low radio luminosity of $L_{\rm 1.4GHz}$ = 1.12$\times$10$^{22}$ W Hz$^{-1}$, two orders of magnitude smaller than other known spiral DRAGNs. We suggest that this may indicate the existence of a previously unknown low-luminosity population of spiral DRAGNS.
We derive a free-form mass distribution for the unrelaxed cluster A370 (z=0.375), using the latest Hubble Frontier Fields images and GLASS spectroscopy. Starting from a reliable set of 10 multiply lensed systems we produce a free-form lens model that identifies ~ 80 multiple-images. Good consistency is found between models using independent subsamples of these lensed systems, with detailed agreement for the well resolved arcs. The mass distribution has two very similar concentrations centred on the two prominent Brightest Cluster Galaxies (or BCGs), with mass profiles that are accurately constrained by a uniquely useful system of long radially lensed images centred on both BCGs. We show that the lensing mass profiles of these BCGs are mainly accounted for by their stellar mass profiles, with a modest contribution from dark matter within r<100 kpc of each BCG. This conclusion may favour a cooled cluster gas origin for BCGs, rather than via mergers of normal galaxies for which dark matter should dominate over stars. Growth via merging between BCGs is, however, consistent with this finding, so that stars still dominate over dark matter .
The Milky Way (MW) and M31 both harbor massive satellite galaxies, the Large Magellanic Cloud (LMC) and M33, which may comprise up to 10 per cent of their host's total mass. Massive satellites can change the orbital barycentre of the host-satellite system by tens of kiloparsecs and are cosmologically expected to harbor dwarf satellite galaxies of their own. Assessing the impact of these effects depends crucially on the orbital histories of the LMC and M33. Here, we revisit the dynamics of the MW-LMC system and present the first detailed analysis of the M31-M33 system utilizing high precision proper motions and statistics from the dark matter-only Illustris cosmological simulation. With the latest Hubble Space Telescope proper motion measurements of M31, we reliably constrain M33's interaction history with its host. In particular, like the LMC, M33 is either on its first passage (t_{inf} < 2 Gyr ago) or if M31 is massive (>=2x10^12 Msun), it is on a long period orbit of about 6 Gyr. Cosmological analogs of the LMC and M33 identified in Illustris support this picture and provide further insight about their host masses. We conclude that, cosmologically, massive satellites like the LMC and M33 are likely completing their first orbits about their hosts. We also find that the orbital energies of such analogs prefer a MW halo mass ~1.5x10^12 Msun and an M31 halo mass >=1.5x10^12 Msun. Despite conventional wisdom, we conclude it is highly improbable that M33 made a close (< 100 kpc) approach to M31 recently ( t_{peri} < 3 Gyr ago). Such orbits are rare (< 1 per cent) within the 4$\sigma$ error space allowed by observations. This conclusion cannot be explained by perturbative effects through four body encounters between the MW, M31, M33, and the LMC. This surprising result implies that we must search for a new explanation for M33's strongly warped gas and stellar discs.
We observe Arp 220, the nearest Ultra-Luminous Infrared Galaxy (ULIRG), over 4 GHz in the K and Ka bands. We provide constraints for the kinematics,morphology, and identify molecular species on scales resolving both nuclei (0.6" or 230 pc). We detect multiple molecular species, including hydroxyl in both cores. We tentatively detect H2O at 21.84 GHz in both nuclei, indicating the likely presence of maser emission. The observed frequency range also contains metastable ammonia transitions from (J,K) = (1,1) to (5,5), as well as the (9,9) inversion line, which, together are a well-known thermometer of dense molecular gas. Furthermore, the non-metastable (4,2) and (10,9) and possibly the (3,1) lines are also detected. We apply a standard temperature analysis to Arp 220. However, the analysis is complicated in that standard LTE assumptions do not hold. There are indications that a substantial fraction of ammonia could be in the non-metastable transitions as opposed to only the metastable ones. Thus, the non-metastable transitions could be essential to constraining the temperature. We compare all of these data to ALMA observations of this source, confirming the outflow previously observed by other tracers in both nuclei.
We use the Wide-field Infrared Survey Explorer (WISE) and the Sloan Digital Sky Survey (SDSS) to confirm a connection between dust-obscured active galactic nuclei (AGNs) and galaxy merging. Using a new, volume-limited (z <= 0.08) catalog of visually-selected major mergers and galaxy-galaxy interactions from the SDSS, with stellar masses above 2x10^10 Msun, we find that major mergers (interactions) are 5-17 (3-5) times more likely to have red [3.4]-[4.6] colors associated with dust-obscured or `dusty' AGNs, compared to non-merging galaxies with similar masses. Using published fiber spectral diagnostics, we map the [3.4]-[4.6] versus [4.6]-[12] colors of different emission-line galaxies and find one-quarter of Seyferts have colors indicative of a dusty AGN. We find that AGNs are five times more likely to be obscured when hosted by a merging galaxy, half of AGNs hosted by a merger are dusty, and we find no enhanced frequency of optical AGNs in merging over non-merging galaxies. We conclude that undetected AGNs missed at shorter wavelengths are at the heart of the ongoing AGN-merger connection debate. The vast majority of mergers hosting dusty AGNs are star-forming and located at the centers of Mhalo<10^13 Msun groups. Assuming plausibly short duration dusty-AGN phases, we speculate that a large fraction of gas-rich mergers experience a brief obscured AGN phase, in agreement with the strong connection between central star formation and black hole growth seen in merger simulations.
We analyze photometry from deep B-band images of 59 void galaxies in the Void Galaxy Survey (VGS), together with their near-infrared 3.6$\mu$m and 4.5$\mu$m Spitzer photometry. The VGS galaxies constitute a sample of void galaxies that were selected by a geometric-topological procedure from the SDSS DR7 data release, and which populate the deep interior of voids. Our void galaxies span a range of absolute B-magnitude from $\rm{M_B=-15.5}$ to $\rm{M_B=-20}$, while at the 3.6$\mu$m band their magnitudes range from $\rm{M_{3.6}=-18}$ to $\rm{M_{3.6}=-24}$. Their B-[3.6] colour and structural parameters indicate these are star forming galaxies. A good reflection of the old stellar population, the near-infrared band photometry also provide a robust estimate of the stellar mass, which for the VGS galaxies we confirm to be smaller than $3 \times 10^{10}$ M$_\odot$. In terms of the structural parameters and morphology, our findings align with other studies in that our VGS galaxy sample consists mostly of small late-type galaxies. Most of them are similar to Sd-Sm galaxies, although a few are irregularly shaped galaxies. The sample even includes two early-type galaxies, one of which is an AGN. Their S\'{e}rsic indices are nearly all smaller than $n=2$ in both bands and they also have small half-light radii. In all, we conclude that the principal impact of the void environment on the galaxies populating them mostly concerns their low stellar mass and small size.
New accurate and homogeneous optical UBVRI photometry has been obtained for
variable stars in the Galactic globular $\omega$ Cen (NGC 5139). We secured
8202 CCD images covering a time interval of 24 years and a sky area of 84x48
arcmin. The current data were complemented with data available in the
literature and provided new, homogeneous pulsation parameters (mean magnitudes,
luminosity amplitudes,periods) for 187 candidate $\omega$ Cen RR Lyrae (RRLs).
Among them we have 101 RRc (first overtone), 85 RRab (fundamental) and a single
candidate RRd (double-mode) variables. Candidate Blazhko RRLs show periods and
colors that are intermediate between RRc and RRab variables, suggesting that
they are transitional objects.
The comparison of the period distribution and of the Bailey diagram indicates
that RRLs in $\omega$ Cen show a long-period tail not present in typical
Oosterhoff II (OoII) globulars. The RRLs in dwarf spheroidals and in ultra
faint dwarfs have properties between Oosterhoff intermediate and OoII clusters.
Metallicity plays a key role in shaping the above evidence. These findings do
not support the hypothesis that $\omega$ Cen is the core remnant of a spoiled
dwarf galaxy.
Using optical Period-Wesenheit relations that are reddening-free and
minimally dependent on metallicity we find a mean distance to $\omega$ Cen of
13.71$\pm$0.08$\pm$0.01 mag (semi-empirical and theoretical calibrations).
Finally, we invert the I-band Period-Luminosity-Metallicity relation to
estimate individual RRLs metal abundances. The metallicity distribution agrees
quite well with spectroscopic and photometric metallicity estimates available
in the literature.
This paper continues our study of the foreground population to the Orion
molecular clouds. The goal is to characterize the foreground population north
of NGC 1981 and to investigate the star formation history in the large Orion
star-forming region. We focus on a region covering about 25 square degrees,
centered on the $\epsilon$ Orionis supergiant (HD 37128, B0\,Ia) and covering
the Orion Belt asterism.
We used a combination of optical (SDSS) and near-infrared (2MASS) data,
informed by X-ray (\textit{XMM-Newton}) and mid-infrared (WISE) data, to
construct a suite of color-color and color-magnitude diagrams for all available
sources. We then applied a new statistical multiband technique to isolate a
previously unknown stellar population in this region.
We identify a rich and well-defined stellar population in the surveyed region
that has about 2\,000 objects that are mostly M stars. We infer the age for
this new population to be at least 5\, Myr and likely $\sim10$\,Myr and
estimate a total of about 2\,500 members, assuming a normal IMF. This new
population, which we call the Orion Belt population, is essentially
extinction-free, disk-free, and its spatial distribution is roughly centered
near $\epsilon$ Ori, although substructure is clearly present.
The Orion Belt population is likely the low-mass counterpart to the Ori OB Ib
subgroup. Although our results do not rule out Blaauw's sequential star
formation scenario for Orion, we argue that the recently proposed blue streams
scenario provides a better framework on which one can explain the Orion star
formation region as a whole. We speculate that the Orion Belt population could
represent the evolved counterpart of an Orion nebula-like cluster.
We aim at performing a kinematic census of young stellar objects (YSOs) in the Rho Ophiuchi F core and partially in the E core of the L1688 dark cloud. We run a proper motion program at the ESO New Technology Telescope (NTT) with the Son of ISAAC (SOFI) instrument over nine years in the near-infrared. We complemented these observations with various public image databases to enlarge the time base of observations and the field of investigation to 0.5 deg X 0.5 deg. We derived positions and proper motions for 2213 objects. From these, 607 proper motions were derived from SOFI observations with a ~1.8 mas/yr accuracy while the remaining objects were measured only from auxiliary data with a mean precision of about ~3 mas/yr. We performed a kinematic analysis of the most accurate proper motions derived in this work, which allowed us to separate cluster members from field stars and to derive the mean properties of the cluster. From the kinematic analysis we derived a list of 68 members and 14 candidate members, comprising 26 new objects with a high membership probability. These new members are generally fainter than the known ones. We measured a mean proper motion of (mu_RA*, mu_DEC)=(-8.2, -24.3)+/-0.8 mas/yr for the L1688 dark cloud. A supervised classification was applied to photometric data of members to allocate a spectral energy distribution (SED) classification to the unclassified members.} We kinematically confirmed that the 56 members that were known from previous studies of the Rho Ophiuchi F cluster and that were also part of our survey are members of the cluster, and we added 26 new members. We defined the evolutionary status of the unclassified members of the cluster. We showed that a large part (23) of these new members are probably brown dwarfs, which multiplies the number of known substellar objects in the cluster by a factor of 3.3.
The detection of complex organic molecules (COMs) toward cold sources such as pre-stellar cores (with T<10 K), has challenged our understanding of the formation processes of COMs in the interstellar medium. Recent modelling on COM chemistry at low temperatures has provided new insight into these processes predicting that COM formation depends strongly on parameters such as visual extinction and the level of CO freeze out. We report deep observations of COMs toward two positions in the L1544 pre-stellar core: the dense, highly-extinguished continuum peak with Av>=30 mag within the inner 2700 au; and a low-density shell with average Av~7.5-8 mag located at 4000 au from the core's center and bright in CH3OH. Our observations show that CH3O, CH3OCH3 and CH3CHO are more abundant (by factors ~2-10) toward the low-density shell than toward the continuum peak. Other COMs such as CH3OCHO, c-C3H2O, HCCCHO, CH2CHCN and HCCNC show slight enhancements (by factors <=3) but the associated uncertainties are large. This suggests that COMs are actively formed and already present in the low-density shells of pre-stellar cores. The modelling of the chemistry of O-bearing COMs in L1544 indicates that these species are enhanced in this shell because i) CO starts freezing out onto dust grains driving an active surface chemistry; ii) the visual extinction is sufficiently high to prevent the UV photo-dissociation of COMs by the external interstellar radiation field; and iii) the density is still moderate to prevent severe depletion of COMs onto grains.
We present an X-ray photometric analysis of six gravitationally lensed quasars spanning from 5 to 14 years, measuring the total (0.83-21.8 keV restframe), soft (0.83-3.6 keV), and hard (3.6-21.8 keV) band image flux ratios for each epoch. Using the ratios of the model-predicted macro-magnifications as baselines, we build differential microlensing curves and obtain joint likelihood functions for the average X-ray emission region sizes. Our analysis yields a Probability Distribution Function for the average half-light radius of the X-Ray emission region in the sample that peaks slightly above 1 gravitational radius, and yields nearly indistinguishable 68 % confidence (one-sided) upper limits of 17.8 (18.9) gravitational radii for the soft (hard) X-ray emitting region, assuming a mean stellar mass of 0.3 solar masses. We see hints of energy dependent microlensing between the soft and hard bands in two of the objects. In a separate analysis on the root-mean-square (RMS) of the microlensing variability, we find significant differences between the soft and hard bands, but the sign of the difference is not consistent across the sample. This suggests the existence of some kind of spatial structure to the X-ray emission in an otherwise extremely compact source. We also discover a correlation between the RMS microlensing variability and the average microlensing amplitude.
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We examine the spatial distribution of the oldest and most metal poor stellar populations of Milky Way-sized galaxies using the APOSTLE cosmological hydrodynamical simulations of the Local Group. In agreement with earlier work, we find strong radial gradients in the fraction of the oldest (tform < 0.8 Gyr) and most metal poor ([Fe/H]< -2.5) stars, both of which increase outwards. The most metal poor stars form over an extended period of time; half of them form after z = 5.3, and the last 10% after z = 2.8. The age of the metal poor stellar population also shows significant variation with environment; a high fraction of them are old in the galaxy's central regions and an even higher fraction in some individual dwarf galaxies, with substantial scatter from dwarf to dwarf. Overall, over half of the stars that belong to both the oldest and most metal-poor population are found outside the solar circle. Somewhat counter-intuitively, we find that dwarf galaxies with a large fraction of metal poor stars that are very old are systems where metal poor stars are relatively rare, but where a substantial old population is present. Our results provide guidance for interpreting the results of surveys designed to hunt for the earliest and most pristine stellar component of our Milky Way.
We investigate the recent star formation history (SFH) in the inner region of 57 nearly face-on spiral galaxies selected from the Calar Alto Legacy Integral Field Area (CALIFA) survey. For each galaxy we use the integral field spectroscopy from CALIFA to obtain two-dimensional maps and radial profiles of three parameters that are sensitive indicators of the recent SFH: the 4000\AA\ break (D$_n$(4000)), and the equivalent width of H$\delta$ absorption (EW(H$\delta_A$)) and H$\alpha$ emission (EW(H$\alpha$)). We have also performed photometric decomposition of bulge/bar/disk components based on SDSS optical image. We identify a class of 17 "turnover" galaxies whose central region present significant drop in D$_n$(4000), and most of them correspondingly show a central upturn in EW(H$\delta_A$) and EW(H$\alpha$). This indicates that the central region of the turnover galaxies has experienced star formation in the past 1-2 Gyr, which makes the bulge younger and more star-forming than surrounding regions. We find almost all (15/17) the turnover galaxies are barred, while only half of the barred galaxies in our sample (15/32) are classified as a turnover galaxy. This finding provides strong evidence in support of the theoretical expectation that the bar may drive gas from the disc inward to trigger star formation in galaxy center, an important channel for the growth/rejuvenation of pseudobulges in disc galaxies.
The enormous velocities of the so called hypervelocity stars (HVSs) derive, likely, from close interactions with massive black holes, binary stars encounters or supernova explosions. In this paper, we investigate the origin of hypervelocity stars as consequence of the close interaction between the Milky Way central massive black hole and a passing-by young stellar cluster. We found that both single and binary HVSs may be generated in a burst-like event, as the cluster passes near the orbital pericentre. High velocity stars will move close to the initial cluster orbital plane and in the direction of the cluster orbital motion at the pericentre. The binary fraction of these HVS jets depends on the primordial binary fraction in the young cluster. The level of initial mass segregation determines the value of the average mass of the ejected stars. Some binary stars will merge, continuing their travel across and out of the Galaxy as blue stragglers.
Cold Fronts and shocks are hallmarks of the complex intra-cluster medium (ICM) in galaxy clusters. They are thought to occur due to gas motions within the ICM and are often attributed to galaxy mergers within the cluster. Using hydro-cosmological simulations of clusters of galaxies, we show that collisions of inflowing gas streams, seen to penetrate to the very centre of about half the clusters, offer an additional mechanism for the formation of shocks and cold fronts in cluster cores. Unlike episodic merger events, a gas stream inflow persists over a period of several Gyrs and it could generate a particular pattern of multiple cold fronts and shocks.
The angular resolution (~10") achieved by the Herschel Space Observatory ~3.5m telescope at FIR wavelengths allowed us to roughly separate the emission toward the inner parsec of the galaxy (the central cavity) from that of the surrounding circumnuclear disk (the CND). The FIR spectrum toward SgrA* is dominated by intense [Oiii], [Oi], [Cii], [Niii], [Nii], and [Ci] fine-structure lines (in decreasing order of luminosity) arising in gas irradiated by the strong UV field from the central stellar cluster. The high-J CO rotational line intensities observed at the interface between the inner CND and the central cavity are consistent with a hot isothermal component at T~10^{3.1} K and n(H_2)~10^4 cm^{-3}. They are also consistent with a distribution of lower temperatures at higher gas density, with most CO at T~300 K. The hot CO component (either the bulk of the CO column density or just a small fraction depending on the above scenario) likely results from a combination of UV and shock-driven heating. Although this component is beam diluted in our FIR observations, it may be resolved at much higher angular resolution. An ALMA project using different molecular tracers to characterize UV-irradiated shocks in the innermost layers of the CND is ongoing.
We analyze the relationships between atomic, neutral hydrogen (HI) and star formation (SF) in the 12 low-mass SHIELD galaxies. We compare high spectral (~0.82 km/s/channel) and spatial resolution (physical resolutions of 170 pc - 700 pc) HI imaging from the VLA with H\alpha and far-ultraviolet imaging. We quantify the degree of co-spatiality between star forming regions and regions of high HI column densities. We calculate the global star formation efficiencies (SFE, $\Sigma_{\rm SFR}$ / $\Sigma_{\rm HI}$), and examine the relationships among the SFE and HI mass, HI column density, and star formation rate (SFR). The systems are consuming their cold neutral gas on timescales of order a few Gyr. While we derive an index for the Kennicutt-Schmidt relation of N ~ 0.68 $\pm$ 0.04 for the SHIELD sample as a whole, the values of N vary considerably from system to system. By supplementing SHIELD results with those from other surveys, we find that HI mass and UV-based SFR are strongly correlated over five orders of magnitude. Identification of patterns within the SHIELD sample allows us to bin the galaxies into three general categories: 1) mainly co-spatial HI and SF regions, found in systems with highest peak HI column densities and highest total HI masses, 2) moderately correlated HI and SF regions, found in systems with moderate HI column densities, and 3) obvious offsets between HI and SF peaks, found in systems with the lowest total HI masses. SF in these galaxies is dominated by stochasticity and random fluctuations in their ISM.
We present kinematic analyses of the 12 galaxies in the "Survey of HI in Extremely Low-mass Dwarfs" (SHIELD). We use multi-configuration interferometric observations of the HI 21cm emission line from the Karl G. Jansky Very Large Array (VLA) to produce image cubes at a variety of spatial and spectral resolutions. Both two- and three-dimensional fitting techniques are employed in an attempt to derive inclination-corrected rotation curves for each galaxy. In most cases, the comparable magnitudes of velocity dispersion and projected rotation result in degeneracies that prohibit unambiguous circular velocity solutions. We thus make spatially resolved position-velocity cuts, corrected for inclination using the stellar components, to estimate the circular rotation velocities. We find circular velocities <30 km/s for the entire survey population. Baryonic masses are calculated using single-dish HI fluxes from Arecibo and stellar masses derived from HST and Spitzer imaging. Comparison is made with total dynamical masses estimated from the position-velocity analysis. The SHIELD galaxies are then placed on the baryonic Tully-Fisher relation. There exists an empirical threshold rotational velocity <15 km/s, below which current observations cannot differentiate coherent rotation from pressure support. The SHIELD galaxies are representative of an important population of galaxies whose properties cannot be described by current models of rotationally-dominated galaxy dynamics.
Ultra-compact high velocity clouds (UCHVCs) were identified in the ALFALFA HI survey as potential gas-bearing dark matter halos. Here we present higher resolution neutral hydrogen (HI) observations of twelve UCHVCS with the Westerbork Synthesis Radio Telescope (WSRT). The UCHVCs were selected based on a combination of size, isolation, large recessional velocity and high column density as the best candidate dark matter halos. The WSRT data were tapered to image the UCHVCs at 210" (comparable to Arecibo) and 105" angular resolution. In a comparison of the single-dish to interferometer data, we find that the line flux recovered in the WSRT observations is comparable to that from the single-dish ALFALFA data. In addition, any structure seen in the ALFALFA data is reproduced in the WSRT maps at the same angular resolution. At 210'" resolution all the sources are generally compact with a smooth HI morphology, as expected from their identification as UCHVCs. At the higher angular resolution, a majority of the sources break into small clumps contained in a diffuse envelope. These UCHVCs also have no ordered velocity motion and are most likely Galactic halo clouds. We identify two UCHVCs, AGC 198606 and AGC 249525, as excellent galaxy candidates based on maintaining a smooth HI morphology at higher angular resolution and showing ordered velocity motion consistent with rotation. A third source, AGC 249565, lies between these two populations in properties and is a possible galaxy candidate. If interpreted as gas-bearing dark matter halos, the three candidate galaxies have rotation velocities of 8-15 km/s, HI masses of 0.6-50 x 10^5 Msun, HI radii of 0.3-2 kpc, and dynamical masses of 2-20 x 10^7 Msun for a range of plausible distances. These are the UCHVCs with the highest column density values in the ALFALFA HI data and we suggest this is the best way to identify further candidates.
Based on the recently completed {\it Chandra}/ACIS survey of X-ray point sources in nearby galaxies, we study the X-ray luminosity functions (XLFs) for X-ray point sources in different types of galaxies and the statistical properties of ultraluminous X-ray sources (ULXs). Uniform procedures are developed to compute the detection threshold, to estimate the foreground/background contamination, and to calculate the XLFs for individual galaxies and groups of galaxies, resulting in an XLF library for 343 galaxies of different types. With the large number of surveyed galaxies, we have studied the XLFs and ULX properties across different host galaxy types, and confirm with good statistics that the XLF slope flattens from lenticular ($\alpha\sim1.50\pm0.07$) to elliptical ($\sim1.21\pm0.02$), to spirals ($\sim0.80\pm0.02$), to peculiars ($\sim0.55\pm0.30$), and to irregulars ($\sim0.26\pm0.10$). The XLF break dividing the neutron star and black hole binaries is also confirmed, albeit at quite different break luminosities for different types of galaxies. A radial dependency is found for ellipticals, with a flatter XLF slope for sources located between $D_{25}$ and 2$D_{25}$, suggesting the XLF slopes in the outer region of early-type galaxies are dominated by low-mass X-ray binaries in globular clusters. This study shows that the ULX rate in early-type galaxies is $0.24\pm0.05$ ULXs per surveyed galaxy, on a $5\sigma$ confidence level. The XLF for ULXs in late-type galaxies extends smoothly until it drops abruptly around $4\times10^{40}$ erg s$^{-1}$, and this break may suggest a mild boundary between the stellar black hole population possibly including 30 $M_\odot$ black holes with super-Eddington radiation and intermediate mass black holes.
Classical Cepheids are among the most useful Galactic and nearby extragalactic distance tracers because of their well-defined period--luminosity relations (PLRs). Open cluster (OC) Cepheids are important objects to independently calibrate these PLRs. Based on Data Release 1 of the {\sl VISTA} Variables in the V\'ia L\'actea survey, we have discovered four new, faint and heavily reddened OC Cepheids, including the longest-period OC Cepheid known, ASAS J180342$-$2211.0 in Teutsch 14a. The other OC--Cepheid pairs include NGC 6334 and V0470 Sco, Majaess 170 and ASAS J160125$-$5150.3, and Teutsch 77 and BB Cen. ASAS J180342$-$2211.0, with a period of $\log P = 1.623$ [days] is important to constrain the slope of the PLR. The currently most complete $JHK_{\rm s}$ Galactic Cepheid PLRs are obtained based on a significantly increased sample of 31 OC Cepheids, with associated uncertainties that are improved by 40 per cent compared with previous determinations (in the $J$ band). The NIR PLRs are in good agreement with previous PLRs determined based on other methods.
We investigate the matter distribution of a spiral galaxy with a counter-rotating stellar core, SDSS J1331+3628 (J1331), independently with gravitational lensing and stellar dynamical modelling. By fitting a gravitational potential model to a quadruplet of lensing images around J1331's bulge, we tightly constrain the mass inside the Einstein radius R_ein = (0.91 +/- 0.02)'' (~= 1.83 +/- 0.04 kpc) to within 4%: M_ein = (7.8 +/- 0.3) x 10^10 M_Sun. We model observed long-slit major axis stellar kinematics in J1331's central regions by finding Multi-Gaussian Expansion (MGE) models for the stellar and dark matter distribution that solve the axisymmetric Jeans equations. The lens and dynamical model are independently derived, but in very good agreement with each other around ~R_ein. We find that J1331's center requires a steep total mass-to-light ratio gradient. A dynamical model including an NFW halo (with virial velocity v_200 ~= 240 +/- 40 km/s and concentration c_200 ~= 8 +/- 2) and moderate tangential velocity anisotropy (beta_z ~= -0.4 +/- 0.1) can reproduce the signatures of J1331's counter-rotating core and predict the stellar and gas rotation curve at larger radii. However, our models do not agree with the observed velocity dispersion at large radii. We speculate that the reason could be a non-trivial change in structure and kinematics due to a possible merger event in J1331's recent past.
We present the first single-burst stellar population models which covers the optical and the infrared wavelength range between 3500 and 50000 Angstrom and which are exclusively based on empirical stellar spectra. To obtain these joint models, we combined the extended MILES models in the optical with our new infrared models that are based on the IRTF (Infrared Telescope Facility) library. The latter are available only for a limited range in terms of both age and metallicity. Our combined single-burst stellar population models were calculated for ages larger than 1 Gyr, for metallicities between [Fe/H] = -0.40 and 0.26, for initial mass functions of various types and slopes, and on the basis of two different sets of isochrones. They are available to the scientific community on the MILES web page. We checked the internal consistency of our models and compared their colour predictions to those of other models that are available in the literature. Optical and near infrared colours that are measured from our models are found to reproduce the colours well that were observed for various samples of early-type galaxies. Our models will enable a detailed analysis of the stellar populations of observed galaxies.
We present a sample of 45 Damped Lyman-$\alpha$ system (DLA, \nhi\ $ \geq 2 \times 10^{20} {\rm cm}^{-2}$) counterparts (33 detections, 12 upper limits) which host gamma-ray bursts (GRB-DLAs) in order to investigate star-formation and metallicity within galaxies hosting DLAs. Our sample spans $z \sim 2-6$ and is nearly three times larger than any previously detected DLA counterparts survey based on quasar line-of-sight searches (QSO-DLAs). We report star formation rates (SFRs) from rest-frame UV photometry and SED modeling. We find that DLA counterpart SFRs are not correlated with either redshift or HI column density. Thanks to the combination of \hst\ and ground-based observations, we also investigate DLA host star-formation efficiency. Our GRB-DLA counterpart sample spans both higher efficiency and low efficiency star formation regions compared to the local Kennicutt-Schmidt relation, local star formation laws, and $z \sim 3$ cosmological simulations. We also compare the depletion times of our DLA hosts sample to other objects in the local Universe, our sample appears to deviate from the star formation efficiencies measured in local spiral and dwarf galaxies. Furthermore, we find similar efficiencies as local inner disks, SMC, and LBG outskirts. Finally, our enrichment time measurements show a spread of systems with under- and over-abundance of metals which may suggest that these systems had episodic star formation and a metal enrichment/depletion as a result of strong stellar feedback and/or metal inflow/outflow.
We present the Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS), a spectroscopic catalogue of radio sources designed to include the full range of radio AGN populations out to redshift z = 0.8. The catalogue covers roughly 800 square degrees of sky, and provides optical identifications for 19,179 radio sources from the 1.4 GHz Faint Images of the Radio Sky at Twenty-cm (FIRST) survey down to an optical magnitude limit of i_mod < 20.5 in Sloan Digital Sky Survey (SDSS) images. Both galaxies and point-like objects are included, and no colour cuts are applied. In collaboration with the WiggleZ and Galaxy And Mass Assembly (GAMA) spectroscopic survey teams, we have obtained new spectra for over 5,000 objects in the LARGESS sample. Combining these new spectra with data from earlier surveys provides spectroscopic data for 12,329 radio sources in the survey area, of which 10,856 have reliable redshifts. 85% of the LARGESS spectroscopic sample are radio AGN (median redshift z = 0.44), and 15% are nearby star-forming galaxies (median z = 0.08). Low-excitation radio galaxies (LERGs) comprise the majority (83%) of LARGESS radio AGN at z < 0.8, with 12% being high-excitation radio galaxies (HERGs) and 5% radio-loud QSOs. Unlike the more homogeneous LERG and QSO sub-populations, HERGs are a heterogeneous class of objects with relatively blue optical colours and a wide dispersion in mid-infrared colours. This is consistent with a picture in which most HERGs are hosted by galaxies with recent or ongoing star formation as well as a classical accretion disk.
We present $K$-band integral field spectroscopic observations towards 17 massive young stellar objects (YSOs) in the low metallicity Small Magellanic Cloud (SMC) and two YSO candidates in the compact H ii regions N81 and N88 A (also in the SMC). These sources, originally identified using $Spitzer$ photometry and/or spectroscopy, have been resolved into 29 $K$-band continuum sources. By comparing Br$\gamma$ emission luminosities with those presented for a Galactic sample of massive YSOs, we find tentative evidence for increased accretion rates in the SMC. Around half of our targets exhibit emission line (Br$\gamma$, He i and H$_2$) morphologies which extend significantly beyond the continuum source and we have mapped both the emission morphologies and the radial velocity fields. This analysis also reveals evidence for the existence of ionized low density regions in the centre outflows from massive YSOs. Additionally we present an analysis of optical spectra towards a similar sample of massive YSOs in the SMC, revealing that the optical emission is photo-excited and originates near the outer edges of molecular clouds, and is therefore consistent with a high mean-free path of UV photons in the interstellar medium (ISM) of the SMC. Finally, we discuss the sample of YSOs in an evolutionary context incorporating the results of previous infrared and radio observations, as well as the near-infrared and optical observations presented in this work. Our spectroscopic analysis in both the $K$-band and the optical regimes, combined with previously obtained infrared and radio data, exposes differences between properties of massive YSOs in our own Galaxy and the SMC, including tracers of accretion, discs and YSO--ISM interactions.
15 years of XMM-Newton observations have established that ultra-fast, highly ionized winds are common in radio-quiet AGN. A simple theory of Eddington-limited accretion correctly predicts the typical velocity (~0.1c) and high ionization of such winds, with observed flow energy capable of ejecting star-forming gas. With a recent extended XMM-Newton observation of the archetypal UFO, PG1211+143, revealing a more complex flow pattern, we suggest that targetted observations over the next decade offer unique potential for probing the inner accretion disc structure and SMBH growth.
Mean-field galactic dynamo theory is the leading theory to explain the prevalence of regular magnetic fields in spiral galaxies, but its systematic comparison with observations is still incomplete and fragmentary. Here we compare predictions of mean-field dynamo models to observational data on magnetic pitch angle and the strength of the mean magnetic field. We demonstrate that a standard $\alpha^2\Omega$ dynamo model produces pitch angles of the regular magnetic fields of nearby galaxies that are reasonably consistent with available data. The dynamo estimates of the magnetic field strength are generally within a factor of a few of the observational values. Reasonable agreement between theoretical and observed pitch angles generally requires the turbulent correlation time $\tau$ to be in the range 10-20 Myr, in agreement with standard estimates. Moreover, good agreement also requires that the ratio of the ionized gas scale height to root-mean-square turbulent velocity increases with radius. Our results thus widen the possibilities to constrain interstellar medium (ISM) parameters using observations of magnetic fields. This work is a step toward systematic statistical tests of galactic dynamo theory. Such studies are becoming more and more feasible as larger datasets are acquired using current and up-and-coming instruments.
Weak emission-line active galactic nuclei (WLAGNs) are radio-quiet active galactic nuclei (AGNs) that have nearly featureless optical spectra. We investigate the ultraviolet to mid-infrared spectral energy distributions of 73 WLAGNs (0.4<z<3) and find that most of them are similar to normal AGNs. We also calculate the covering factor of warm dust of these 73 WLAGNs. No significant difference is indicated by a KS test between the covering factor of WLAGNs and normal AGNs in the common range of bolometric luminosity. The implication for several models of WLAGNs is discussed. The super-Eddington accretion is unlikely the dominant reason for the featureless spectrum of a WLAGN. The present results favor the evolution scenario, i.e., WLAGNs are in a special stage of AGNs.
We perform two-dimensional axially symmetric radiation-hydrodynamic simulations to assess the impact of outflows and radiative force feedback from massive protostars by varying when the protostellar outflow starts, the ratio of ejection to accretion rates, and the strength of the wide angle disk wind component. The star formation efficiency, i.e. the ratio of final stellar mass to initial core mass, is dominated by radiative forces and the ratio of outflow to accretion rates. Increasing this ratio has three effects: First, the protostar grows slower with a lower luminosity at any given time, lowering radiative feedback. Second, bipolar cavities cleared by the outflow are larger, further diminishing radiative feedback on disk and core scales. Third, the higher momentum outflow sweeps up more material from the collapsing envelope, decreasing the protostar's potential mass reservoir via entrainment. The star formation efficiency varies with the ratio of ejection to accretion rates from 50% in the case of very weak outflows to as low as 20% for very strong outflows. At latitudes between the low density bipolar cavity and the high density accretion disk, wide angle disk winds remove some of the gas, which otherwise would be part of the accretion flow onto the disk; varying the strength of these wide angle disk winds, however, alters the final star formation efficiency by only +/-6%. For all cases, the opening angle of the bipolar outflow cavity remains below 20 degree during early protostellar accretion phases, increasing rapidly up to 65 degree at the onset of radiation pressure feedback.
We present the results of SPT-GMOS, a spectroscopic survey with the Gemini Multi-Object Spectrograph (GMOS) on Gemini South. The targets of SPT-GMOS are galaxy clusters identified in the SPT-SZ survey, a millimeter-wave survey of 2500 squ. deg. of the southern sky using the South Pole Telescope (SPT). Multi-object spectroscopic observations of 62 SPT-selected galaxy clusters were performed between January 2011 and December 2015, yielding spectra with radial velocity measurements for 2595 sources. We identify 2243 of these sources as galaxies, and 352 as stars. Of the galaxies, we identify 1579 as members of SPT-SZ galaxy clusters. The primary goal of these observations was to obtain spectra of cluster member galaxies to estimate cluster redshifts and velocity dispersions. We describe the full spectroscopic dataset and resulting data products, including galaxy redshifts, cluster redshifts and velocity dispersions, and measurements of several well-known spectral indices for each galaxy: the equivalent width, W, of [O II] 3727,3729 and H-delta, and the 4000A break strength, D4000. We use the spectral indices to classify galaxies by spectral type (i.e., passive, post-starburst, star-forming), and we match the spectra against photometric catalogs to characterize spectroscopically-observed cluster members as a function of brightness (relative to m*). Finally, we report several new measurements of redshifts for ten bright, strongly-lensed background galaxies in the cores of eight galaxy clusters. Combining the SPT-GMOS dataset with previous spectroscopic follow-up of SPT-SZ galaxy clusters results in spectroscopic measurements for >100 clusters, or ~20% of the full SPT-SZ sample.
Intrinsic colors of normal stars are derived in the popularly used infrared bands involving the 2MASS/JHKs, WISE, Spitzer/IRAC and AKARI/S9W filters. Based on three spectroscopic surveys -- LAMOST, RAVE and APOGEE, stars are classified into groups of giants and dwarfs, as well as metal-normal and metal-poor stars. An empirical analytical relation of the intrinsic color is obtained with stellar effective temperature (Teff) for each group of stars after the zero-reddening stars are selected from the blue edge in the $J-\lambda$ versus (Teff) diagram. It is found that metallicity has little effect on the infrared colors. In the near-infrared bands, our results agree with previous work. In addition, the color indexes H-W2 and Ks-W1 that are taken as constant to calculate interstellar extinction are discussed. The intrinsic color of M-type stars are derived separately due to lack of accurate measurement of their effective temperature.
We are pursuing a project to build a database of phase calibration sources suitable for Giant Metrewave Radio Telescope (GMRT). Here we present the first release of 45 low frequency calibration sources at 235 MHz and 610 MHz. These calibration sources are broadly divided into quasars, radio galaxies and unidentified sources. We provide their flux densities, models for calibration sources, (u,v) plots, final deconvolved restored maps and clean-component lists/files for use in the Astronomical Image Processing System (AIPS) and the Common Astronomy Software Applications (CASA). We also assign a quality factor to each of the calibration sources. These data products are made available online through the GMRT observatory website. In addition we find that (i) these 45 low frequency calibration sources are uniformly distributed in the sky and future efforts to increase the size of the database should populate the sky further, (ii) spectra of these calibration sources are about equally divided between straight, curved and complex shapes, (iii) quasars tend to exhibit flatter radio spectra as compared to the radio galaxies or the unidentified sources, (iv) quasars are also known to be radio variable and hence possibly show complex spectra more frequently, and (v) radio galaxies tend to have steeper spectra, which are possibly due to the large redshifts of distant galaxies causing the shift of spectrum to lower frequencies.
In conjunction with ab initio potential energy and dipole moment surfaces for the electronic ground state, we have made a theoretical study of the radiative lifetimes for the hydronium ion H$_3$O$^{+}$ and its deuterated isotopologues. We compute the ro-vibrational energy levels and their associated wavefunctions together with Einstein coefficients for the electric dipole transitions. A detailed analysis of the stability of the ro-vibrational states have been carried out and the longest-living states of the hydronium ions have been identified. We report estimated radiative lifetimes and cooling functions for temperatures $<$ 200 K. A number of long-living meta-stable states are identified, capable of population trapping.
Main sequence turn-off (MSTO) stars have advantages as indicators of Galactic evolution since their ages could be robustly estimated from atmospheric parameters. Hundreds of thousands of MSTO stars have been selected from the LAMOST Galactic sur- vey to study the evolution of the Galaxy, and it is vital to derive accurate stellar parameters. In this work, we select 150 MSTO star candidates from the MSTO stars sample of Xiang that have asteroseismic parameters and determine accurate stellar parameters for these stars combing the asteroseismic parameters deduced from the Kepler photometry and atmospheric parameters deduced from the LAMOST spectra.With this sample, we examine the age deter- mination as well as the contamination rate of the MSTO stars sample. A comparison of age between this work and Xiang shows a mean difference of 0.53 Gyr (7%) and a dispersion of 2.71 Gyr (28%). The results show that 79 of the candidates are MSTO stars, while the others are contaminations from either main sequence or sub-giant stars. The contamination rate for the oldest stars is much higher than that for the younger stars. The main cause for the high contamination rate is found to be the relatively large systematic bias in the LAMOST surface gravity estimates.
We present new deep UBVRI images and high-resolution multi-object optical spectroscopy of the young (~ 6 - 10 Myr old), relatively nearby (800 pc) open cluster IC 2395. We identify nearly 300 cluster members and use the photometry to estimate their spectral types, which extend from early B to middle M. We also present an infrared imaging survey of the central region using the IRAC and MIPS instruments on board the Spitzer Space Telescope, covering the wavelength range from 3.6 to 24 microns. Our infrared observations allow us to detect dust in circumstellar disks originating over a typical range of radii ~ 0.1 to ~ 10AU from the central star. We identify 18 Class II, 8 transitional disk, and 23 debris disk candidates, respectively 6.5%, 2.9%, and 8.3% of the cluster members with appropriate data. We apply the same criteria for transitional disk identification to 19 other stellar clusters and associations spanning ages from ~ 1 to ~ 18 Myr. We find that the number of disks in the transitional phase as a fraction of the total with strong 24 micron excesses ([8] - [24] > 1.5) increases from 8.4 +\- 1.3% at ~ 3 Myr to 46 +\- 5% at ~ 10 Myr. Alternative definitions of transitional disks will yield different percentages but should show the same trend.
It has been suggested that the internal dynamics of dwarf spheroidal galaxies (dSphs) can be used to test whether or not ultralight axions with $m_a\sim 10^{-22}\text{eV}$ are a preferred dark matter candidate. However, comparisons to theoretical predictions tend to be inconclusive for the simple reason that while most cosmological models consider only dark matter, one observes only baryons. Here we use realistic kinematic mock data catalogs of Milky Way dSph's to show that the "mass-anisotropy degeneracy" in the Jeans equations leads to biased bounds on the axion mass in galaxies with unknown dark matter halo profiles. In galaxies with multiple chemodynamical components this bias can be partly removed by modelling the mass enclosed within each subpopulation. However, analysis of the mock data reveals that the least-biased constraints on the axion mass result from fitting the luminosity-averaged velocity dispersion of the individual chemodynamical components directly. Applying our analysis to two dSph's with reported stellar subcomponents, Fornax and Sculptor, and assuming that the halo profile has not been acted on by baryons, yields core radii $r_{c}>1.5$ kpc and $r_c> 1.2$ kpc respectively, and $m_a<0.4\times 10^{-22}\text{eV}$ at 97.5\% confidence. These bounds are in tension with the number of observed satellites derived from simple (but conservative) estimates of the subhalo mass function in Milky Way-like galaxies. We discuss how baryonic feedback might affect our results, and the impact of such a small axion mass on the growth of structures in the Universe.
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LkCa 15 is an extensively studied star in the Taurus region known for its pre-transitional disk with a large inner cavity in dust continuum and normal gas accretion rate. The most popular hypothesis to explain the LkCa 15 data invokes one or more planets to carve out the inner cavity, while gas continues to flow across the gap from the outer disk onto the central star. We present spatially unresolved HCO+ J=4-3 observations of the LkCa 15 disk from the JCMT and model the data with the ProDiMo code. We find that: (1) HCO+ line-wings are clearly detected, certifying the presence of gas in the cavity within <50 AU of the star. (2) Reproducing the observed line-wing flux requires both a significant suppression of cavity dust (by a factor >10^4 compared to the ISM) and a substantial increase in the gas scale-height within the cavity (H_0/R_0 ~ 0.6). An ISM dust-to-gas ratio (d:g=10^-2) yields too little line-wing flux regardless of the scale-height or cavity gas geometry, while a smaller scale-height also under predicts the flux even with a reduced d:g. (3) The cavity gas mass is consistent with the surface density profile of the outer disk extended inwards to the sublimation radius (corresponding to mass M_d ~ 0.03 M_sun), and masses lower by a factor >10 appear to be ruled out.
We present the CAlibrating LYMan-$\alpha$ with H$\alpha$ (CALYMHA) pilot survey and new results on Lyman-$\alpha$ (Lya) selected galaxies at z~2. We use a custom-built Lya narrow-band filter at the Isaac Newton Telescope, designed to provide a matched volume coverage to the z=2.23 Ha HiZELS survey. Here we present the first results for the COSMOS and UDS fields. Our survey currently reaches a 3$\sigma$ line flux limit of ~4x10$^{-17}$ erg/s/cm$^{2}$, and a Lya luminosity limit of ~10$^{42.3}$ erg/s. We find 188 Lya emitters over 7.3x10$^5$ Mpc$^{3}$, but also find significant numbers of other line emitting sources corresponding to HeII, CIII] and CIV emission lines. These sources are important contaminants, and we carefully remove them, unlike most previous studies. We find that the Lya luminosity function at z=2.23 is very well described by a Schechter function up to L~10$^{43}$ erg/s with L$^*=10^{42.59+-0.05}$ erg/s, $\phi^*=10^{-3.09+-0.08}$ Mpc$^{-3}$ and $\alpha$=-1.75+-0.15. Above L~10$^{43}$ erg/s the Lya luminosity function becomes power-law like, driven by X-ray AGN. We find that Lya-selected emitters have a high escape fraction of 37+-7%, anti-correlated with Lya luminosity and correlated with Lya equivalent width. Lya emitters have ubiquitous large (~40 kpc) Lya haloes, 2x larger than their Ha extents. By directly comparing our Lya and Ha luminosity functions we find that the global/overall escape fraction of Lya photons (within a 13 kpc radius) from the full population of star-forming galaxies is 5.1+-0.2% at the peak of the star formation history. An extra 3.3+-0.3% of Lya photons likely still escape, but at larger radii.
Coevolution between supermassive black holes (BHs) and their host galaxies is universally adopted in models for galaxy formation. In the absence of feedback from active galactic nuclei, simulated massive galaxies keep forming stars in the local Universe. From an observational point of view, however, such coevolution remains unclear. We present a stellar population analysis of galaxies with direct BH mass measurements and the BH mass-{\sigma} relation as a working framework. We find that over-massive BH galaxies, i.e., galaxies lying above the best-fitting BH mass-{\sigma} line, tend to be older and more {\alpha}-element enhanced than under-massive BH galaxies. The scatter in the BH mass-{\sigma}-[{\alpha}/Fe] plane is significantly lower than in the standard BH mass-{\sigma} relation. We interpret this trend as an imprint of active galactic nucleus feedback on the star formation histories of massive galaxies.
We investigate the reliability of mass estimators based on the observable velocity dispersion and half-light radius $R_\mathrm{h}$ for dispersion-supported galaxies. We show how to extend them to flattened systems and provide simple formulae for the mass within an ellipsoid under the assumption the dark matter density and the stellar density are stratified on the same self-similar ellipsoids. We demonstrate explicitly that the spherical mass estimators (Walker et al. 2009, Wolf et al. 2010) give accurate values for the mass within the half-light ellipsoid, provided $R_\mathrm{h}$ is replaced by its `circularized' analogue $R_\mathrm{h}\sqrt{1-\epsilon}$. We provide a mathematical justification for this surprisingly simple and effective workaround. It means, for example, that the mass-to-light ratios are valid not just when the light and dark matter are spherically distributed, but also when they are flattened on ellipsoids of the same constant shape.
We examine the properties of barred disc galaxies in a LCDM cosmological hydrodynamical simulation from the EAGLE project. Our study follows the formation of 269 discs identified at z = 0 in the stellar mass range 10.6 < log Mstr /M < 11. These discs show a wide range of bar strengths, from unbarred discs to weak bars to strongly barred systems (= 20%). Bars in these systems develop after redshift = 1.3, on timescales that depend sen- sitively on the strength of the pattern. Strong bars develop relatively quickly (in a few Gyr, = 10 disc rotation periods) in systems that are disc dominated, gas poor, and have declining rotation curves. Weak bars develop more slowly in systems where the disc is less gravitation- ally important, and are still growing at z = 0. Unbarred galaxies are comparatively gas-rich discs whose rotation speeds do not exceed the maximum circular velocity of the halos they inhabit. Bar lengths compare favourably with observations, ranging from 0.2 to 0.8 times the radius containing 90% of the stars. Bars slow down remarkably quickly as they grow, causing the inner regions of the surrounding dark halo to expand. At z = 0 strong bars have corota- tion radii roughly ten times the bar length. Such slow bars are inconsistent with the few cases where pattern speeds have been measured or inferred observationally, a discrepancy that, if confirmed, might prove a challenge for disc galaxy formation in LCDM.
Star formation is primarily controlled by the interplay between gravity, turbulence, and magnetic fields. However, the turbulence and magnetic fields in molecular clouds near the Galactic Center may differ substantially from spiral-arm clouds. Here we determine the physical parameters of the central molecular zone (CMZ) cloud G0.253+0.016, its turbulence, magnetic field and filamentary structure. Using column-density maps based on dust-continuum emission observations with ALMA+Herschel, we identify filaments and show that at least one dense core is located along them. We measure the filament width W_fil=0.17$\pm$0.08pc and the sonic scale {\lambda}_sonic=0.15$\pm$0.11pc of the turbulence, and find W_fil~{\lambda}_sonic. A strong velocity gradient is seen in the HNCO intensity-weighted velocity maps obtained with ALMA+Mopra, which is likely caused by large-scale shearing of G0.253+0.016, producing a wide double-peaked velocity PDF. After subtracting the gradient to isolate the turbulent motions, we find a nearly Gaussian velocity PDF typical for turbulence. We measure the total and turbulent velocity dispersion, 8.8$\pm$0.2km/s and 3.9$\pm$0.1km/s, respectively. Using magnetohydrodynamical simulations, we find that G0.253+0.016's turbulent magnetic field B_turb=130$\pm$50$\mu$G is only ~1/10 of the ordered field component. Combining these measurements, we reconstruct the dominant turbulence driving mode in G0.253+0.016 and find a driving parameter b=0.22$\pm$0.12, indicating solenoidal (divergence-free) driving. We compare this to spiral-arm clouds, which typically have a significant compressive (curl-free) driving component (b>0.4). Motivated by previous reports of strong shearing motions in the CMZ, we speculate that shear causes the solenoidal driving in G0.253+0.016 and show that this reduces the star formation rate (SFR) by a factor of 6.9 compared to typical nearby clouds.
We report a correlation between the radial acceleration traced by rotation curves and that predicted by the observed distribution of baryons. The same relation is followed by 2693 points in 153 galaxies with very different morphologies, masses, sizes, and gas fractions. The correlation persists even when dark matter dominates. Consequently, the dark matter contribution is fully specified by that of the baryons. The observed scatter is small and largely dominated by observational uncertainties. This radial acceleration relation is tantamount to a natural law for rotating galaxies.
We present the discovery of a very faint stellar system, SMASH 1, that is potentially a satellite of the Large Magellanic Cloud. Found within the Survey of the MAgellanic Stellar History (SMASH), SMASH 1 is a compact (r_h = 9.1^{+5.9}_{-3.4} pc) and very low luminosity (M_V = -1.0 +/- 0.9, L_V=10^{2.3 +/- 0.4} Lsun) stellar system that is revealed by its sparsely populated main sequence and a handful of red-giant-branch candidate member stars. The photometric properties of these stars are compatible with a metal-poor ([Fe/H]=-2.2) and old (13 Gyr) isochrone located at a distance modulus of ~18.8, i.e. a distance of ~57 kpc. Situated at 11.3{\deg} from the LMC in projection, its 3-dimensional distance from the Cloud is ~13 kpc, consistent with a connection to the LMC, whose tidal radius is at least 16 kpc. Although the nature of SMASH 1 remains uncertain, its compactness favors it being a stellar cluster and hence dark-matter free. If this is the case, its dynamical tidal radius is only <19 pc at this distance from the LMC, and smaller than the system's extent on the sky. Its low luminosity and apparent high ellipticity (\epsilon=0.62^{+0.17}_{-0.21}) with its major axis pointing toward the LMC may well be the tell-tale sign of its imminent tidal demise.
We study the correlation between far-infared/submm dust emission and atomic gas column density in order to derive the properties of the high Galactic latitude, low density, Milky Way cirrus in the foreground of the Virgo cluster of galaxies. Dust emission maps from 60 to 850 um are obtained from SPIRE observations carried out within the Herschel Virgo Cluster Survey, complemented by IRAS-IRIS and Planck-HFI maps. Data from the Arecibo legacy Fast ALFA Survey is used to derive atomic gas column densities for two broad velocity components, low and intermediate velocity clouds. Dust emissivities are derived for each gas component and each far-infared/submm band. For the low velocity clouds, we measure an average emissivity 0.79 +/- 0.08 times 1E-20 MJy sr^-1 cm^2 at 250 um. After fitting a modified blackbody to the available bands, we estimated a dust absorption cross-section 0.49 +/- 0.13 times 1E-25 cm^2 H^-1 at 250 um (with dust temperature T = 20.4 +/- 1.5 K and spectral index beta = 1.53 +/- 0.17). The results are in excellent agreement with those obtained by Planck over a much larger coverage of the high Galactic latitude cirrus (50% of the sky vs 0.2% in our work). For dust associated with intermediate velocity gas, we confirm earlier Planck results and find a higher temperature and lower emissivity and cross-section. After subtracting the modelled components, we find regions at scales smaller than 20' where the residuals deviate significantly from the average, cosmic-infrared-background dominated, scatter. These large residuals are most likely due to local variations in the cirrus dust properties (and/or the dust/atomic-gas correlation) or to high-latitude molecular clouds with average N_H2 <~ 1E20 cm^-2. We find no conclusive evidence for intracluster dust emission in Virgo.
The XQ-100 survey has provided high signal-noise spectra of 100 redshift 3-4.5 quasars with the X-Shooter spectrograph. The metal abundances for 13 elements in the 41 damped Lyman alpha systems (DLAs) identified in the XQ-100 sample are presented, and an investigation into abundances of a variety of DLA classes is conducted. The XQ-100 DLA sample contains five DLAs within 5000 km/s of their host quasar (proximate DLAs; PDLAs) as well as three sightlines which contain two DLAs within 10,000 km/s of each other along the same line-of-sight (multiple DLAs; MDLAs). Combined with previous observations in the literature, we demonstrate that PDLAs with logN(HI)<21.0 show lower [S/H] and [Fe/H] (relative to intervening systems with similar redshift and N(HI)), whilst higher [S/H] and [Si/H] are seen in PDLAs with logN(HI)>21.0. These abundance discrepancies are independent of their line-of-sight velocity separation from the host quasar, and the velocity width of the metal lines (v90). Contrary to previous studies, MDLAs show no difference in [alpha/Fe] relative to single DLAs matched in metallicity and redshift. In addition, we present follow-up UVES data of J0034+1639, a sightline containing three DLAs, including a metal-poor DLA with [Fe/H]=-2.82 (the third lowest [Fe/H] in DLAs identified to date) at z=4.25. Lastly we study the dust-corrected [Zn/Fe], emphasizing that near-IR coverage of X-Shooter provides unprecedented access to MgII, CaII and TiII lines (at redshifts 3-4) to provide additional evidence for subsolar [Zn/Fe] ratio in DLAs.
This automated catalogue combines all the largest published optical, radio and X-ray sky catalogues to find probable radio/X-ray associations to optical objects, plus double radio lobes, using uniform processing against all input data. The total count is 1002855 optical objects so presented. Each object is displayed with J2000 astrometry, optical and radio/X-ray identifiers, red and blue photometry, and calculated probabilities and optical field solutions of the associations. This is the third and final edition of this method.
We present the stellar mass - size relation for 49 galaxies within the $z$ = 1.067 cluster SPT-CL J0546$-$5345, with FWHM $\sim$80-120 mas $K_{\mathrm s}$-band data from the Gemini multi-conjugate adaptive optics system (GeMS/GSAOI). This is the first such measurement in a cluster environment, performed at sub-kpc resolution at rest-frame wavelengths dominated by the light of the underlying old stellar populations. The observed stellar mass - size relation is offset from the local relation by 0.21 dex, corresponding to a size evolution proportional to $(1+z)^{-1.25}$, consistent with the literature. The slope of the stellar mass - size relation $\beta$ = 0.74 $\pm$ 0.06, consistent with the local relation. The absence of slope evolution indicates that the amount of size growth is constant with stellar mass. This suggests that galaxies in massive clusters such as SPT-CL J0546$-$5345 grow via processes that increase the size without significant morphological interference, such as minor mergers and/or adiabatic expansion. The slope of the cluster stellar mass - size relation is significantly shallower if measured in $HST$/ACS imaging at wavelengths blueward of the Balmer break, similar to rest-frame UV relations at $z$ = 1 in the literature. The stellar mass - size relation must be measured at redder wavelengths, which are more sensitive to the old stellar population that dominates the stellar mass of the galaxies. The slope is unchanged when GeMS $K_s$-band imaging is degraded to the resolution of $K$-band HST/NICMOS resolution but dramatically affected when degraded to $K_s$-band Magellan/FourStar resolution. Such measurements must be made with AO in order to accurately characterise the sizes of compact, $z$ = 1 galaxies.
The European Space Agency has invested heavily in two cornerstones missions; Herschel and Planck. The legacy data from these missions provides us with an unprecedented opportunity to study cosmic dust in galaxies so that we can answer fundamental questions about, for example: the origin of the chemical elements, physical processes in the interstellar medium (ISM), its effect on stellar radiation, its relation to star formation and how this relates to the cosmic far infrared background. In this paper we describe the DustPedia project, which is enabling us to develop tools and computer models that will help us relate observed cosmic dust emission to its physical properties (chemical composition, size distribution, temperature), to its origins (evolved stars, super novae, growth in the ISM) and the processes that destroy it (high energy collisions and shock heated gas). To carry out this research we will combine the Herschel/Planck data with that from other sources of data, providing observations at numerous wavelengths (< 41) across the spectral energy distribution, thus creating the DustPedia database. To maximise our spatial resolution and sensitivity to cosmic dust we limit our analysis to 4231 local galaxies (v < 3000 km/s) selected via their near infrared luminosity (stellar mass). To help us interpret the data we have developed a new physical model for dust (THEMIS), a new Bayesian method of fitting and interpreting spectral energy distributions (HerBIE) and a state-of-the-art Monte Carlo photon tracing radiative transfer model (SKIRT). In this the first of the DustPedia papers we describe the project objectives, data sets used and provide an insight into the new scientific methods we plan to implement.
We obtained Arecibo HI line follow-up observations of 154 of the 2600 galaxies in the Nan\c{c}ay Interstellar Baryons Legacy Extragalactic Survey (NIBLES) sample. These observations are on average four times more sensitive than the original observations at the Nan\c{c}ay Radio Telescope. The main goal of this survey is to characterize the underlying HI properties of the NIBLES galaxies which were undetected or marginally detected at Nan\c{c}ay. Of the Nan\c{c}ay non-detections, 85% were either clearly or marginally detected at Arecibo, while 89% of the Nan\c{c}ay marginal detections were clearly detected. Based on the statistics of the detections relative to g-i color and r-band luminosity (L$_r$) distribution among our Arecibo observations, we anticipate ~60% of our 867 Nan\c{c}ay non-detections and marginal detections could be detected at the sensitivity of our Arecibo observations. Follow-up observations of our low luminosity (L$_r$ < 10$^{8.5}$ L$_{\odot}$) blue sources indicate that they have, on average, more concentrated stellar mass distributions than the Nan\c{c}ay detections in the same luminosity range, suggesting we may be probing galaxies with intrinsically different properties. These follow-up observations enable us to probe HI mass fractions, log($M_{\rm HI}$/$M_{\star}$) 0.5 dex and 1 dex lower, on average, than the NIBLES and ALFALFA surveys respectively.
We present a hierarchical Bayesian method for estimating the total mass and mass profile of the Milky Way Galaxy. The new hierarchical Bayesian approach further improves the framework presented by Eadie, Harris, & Widrow (2015) and Eadie & Harris (2016) and builds upon the preliminary reports by Eadie et al (2015a,c). The method uses a distribution function $f(\mathcal{E},L)$ to model the galaxy and kinematic data from satellite objects such as globular clusters to trace the Galaxy's gravitational potential. A major advantage of the method is that it not only includes complete and incomplete data simultaneously in the analysis, but also incorporates measurement uncertainties in a coherent and meaningful way. We first test the hierarchical Bayesian framework, which includes measurement uncertainties, using the same data and power-law model assumed in Eadie & Harris (2016), and find the results are similar but more strongly constrained. Next, we take advantage of the new statistical framework and incorporate all possible globular cluster data, finding a cumulative mass profile with Bayesian credible regions. This profile implies a mass within $125$kpc of $4.81\times 10^{11} M_{\odot}$ with a 95\% Bayesian credible region of $(3.96-5.76)\times10^{11}M_{\odot}$.
In this chapter I review the effects of supernovae explosions on the
dynamical evolution of (1) binary stars and (2) star clusters.
(1) Supernovae in binaries can drastically alter the orbit of the system,
sometimes disrupting it entirely, and are thought to be partially responsible
for `runaway' massive stars - stars in the Galaxy with large peculiar
velocities. The ejection of the lower-mass secondary component of a binary
occurs often in the event of the more massive primary star exploding as a
supernova. The orbital properties of binaries that contain massive stars mean
that the observed velocities of runaway stars (10s - 100s km s$^{-1}$) are
consistent with this scenario.
(2) Star formation is an inherently inefficient process, and much of the
potential in young star clusters remains in the form of gas. Supernovae can in
principle expel this gas, which would drastically alter the dynamics of the
cluster by unbinding the stars from the potential. However, recent numerical
simulations, and observational evidence that gas-free clusters are observed to
be bound, suggest that the effects of supernova explosions on the dynamics of
star clusters are likely to be minimal.
Aims: for the first time the astrometric capabilities of the Multi-Conjugate Adaptive Optics (MCAO) facility GeMS with the GSAOI camera on Gemini-South are tested to quantify the accuracy in determining stellar proper motions in the Galactic globular cluster NGC 6681. Methods: proper motions from HST/ACS for a sample of its stars are already available, and this allows us to construct a distortion-free reference at the epoch of GeMS observations that is used to measure and correct the temporally changing distortions for each GeMS exposure. In this way, we are able to compare the corrected GeMS images with a first-epoch of HST/ACS images to recover the relative proper motion of the Sagittarius dwarf spheroidal galaxy with respect to NGC 6681. Results: we find this to be (\mu_{\alpha}cos\delta, \mu_{\delta}) = (4.09,-3.41) mas/yr, which matches previous HST/ACS measurements with a very good accuracy of 0.03 mas/yr and with a comparable precision (r.m.s of 0.43 mas/yr). Conclusions: this study successfully demonstrates that high-quality proper motions can be measured for quite large fields of view (85 arcsec X 85 arcsec) with MCAO-assisted, ground-based cameras and provides a first, successful test of the performances of GeMS on multi-epoch data.
We present a time domain waveform model that describes the inspiral, merger and ringdown of compact binary systems whose components are non-spinning, and which evolve on orbits with low to moderate eccentricity. The inspiral evolution is described using third order post-Newtonian equations both for the equations of motion of the binary, and its far-zone radiation field. This latter component also includes instantaneous, tails and tails-of-tails contributions, and a contribution due to non-linear memory. This framework reduces to the post-Newtonian approximant $\texttt{TaylorT4}$ at third post-Newtonian order in the zero eccentricity limit. To improve phase accuracy, we also incorporate higher-order post-Newtonian corrections for the energy flux of quasi-circular binaries and gravitational self-force corrections to the binding energy of compact binaries. This enhanced prescription for the inspiral evolution is combined with a fully analytical prescription for the merger-ringdown evolution constructed using a catalog of numerical relativity simulations. We show that this inspiral-merger-ringdown waveform model reproduces the effective-one-body model of Phys. Rev. D 89, 061501 for black hole binaries with mass-ratios between 1 to 15 in the zero eccentricity limit over a wide range of the parameter space under consideration. We use this model to show that the gravitational wave transients GW150914 and GW151226 can be effectively recovered with template banks of quasi-circular, spin-aligned waveforms if the eccentricity $e_0$ of these systems when they enter the aLIGO band at a gravitational wave frequency of 14 Hz satisfies $e_0^{\rm GW150914}\leq0.15$ and $e_0^{\rm GW151226}\leq0.1$. We also show that quasi-circular, spin-aligned compact binaries define a signal manifold that is predominantly orthogonal to a manifold generated by non-spinning, eccentric signals for $e_0\geq0.1$.
We carry out an ALMA $\rm N_2D^+$(3-2) and 1.3~mm continuum survey towards 32 high mass surface density regions in seven Infrared Dark Clouds with the aim of finding massive starless cores, which may be the initial conditions for the formation of massive stars. Cores showing strong $\rm N_2D^+$(3-2) emission are expected to be highly deuterated and indicative of early, potentially pre-stellar stages of star formation. We also present maps of these regions in ancillary line tracers, including C$^{18}$O(2-1), DCN(3-2) and DCO$^+$(3-2). Over 100 $\rm N_2D^+$ cores are identified with our newly developed core-finding algorithm based on connected structures in position-velocity space. The most massive core has $\gtrsim70\:M_\odot$ (potentially $\sim170\:M_\odot$) and so may be representative of the initial conditions for massive star formation. The existence and dynamical properties of such cores constrain massive star formation theories. We measure the line widths and thus velocity dispersion of six of the cores with strongest $\rm N_2D^+$(3-2) line emission, finding results that are generally consistent with virial equilibrium of pressure confined cores.
In an effort to further our interest in understanding basic chemistry of interstellar molecules, we carry out here an extensive investigation of the stabilities of interstellar carbon chains; Cn, H2Cn, HCnN and CnX (X=N, O, Si, S, H, P, H-, N-). These sets of molecules accounts for about 20% of all the known interstellar and circumstellar molecules, their high abundances therefore demand a serious attention. High level ab initio quantum chemical calculations are employed to accurately estimate enthalpy of formation, chemical reactivity indices; global hardness and softness; and other chemical parameters of these molecules. Chemical modeling of the abundances of these molecular species has also been performed. Of the 89 molecules considered from these groups, 47 have been astronomically observed, these observed molecules are found to be more stable with respect to other members of the group. Of the 47 observed molecules, 60% are odd number carbon chains. Interstellar chemistry is not actually driven by the thermodynamics, it is primarily dependent on various kinetic parameters. However, we found that the detectability of the odd numbered carbon chains could be correlated due to the fact that they are more stable than the corresponding even numbered carbon chains. Based on this aspect, the next possible carbon chain molecule for astronomical observation in each group is proposed. The effect of kinetics in the formation of some of these carbon chain molecules is also discussed.
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We use the combined data from the COS-GASS and COS-Halos surveys to characterize the Circum-Galactic Medium (CGM) surrounding typical low-redshift galaxies in the mass range $\rm~M_*\sim~10^{9.5-11.5}~M_{\odot} $, and over a range of impact parameters extending to just beyond the halo virial radius ($\rm~R_{vir}$). We find the radial scale length of the distributions of the equivalent widths of the Lyman~$\alpha$ and Si III absorbers to be 0.9 and 0.4 $\rm~R_{vir}$, respectively. The radial distribution of equivalent widths is relatively uniform for the blue galaxies, but highly patchy (low covering fraction) for the red galaxies. We also find that the Lyman~$\alpha$ and Si III equivalent widths show significant positive correlations with the specific star-formation rate (sSFR) of the galaxy. We find a surprising lack of correlations between the halo mass (virial velocity) and either the velocity dispersions or velocity offsets of the Lyman~$\alpha$ lines. The ratio of the velocity offset to the velocity dispersion for the Lyman~$\alpha$ absorbers has a mean value of $\sim$ 4, suggesting that a given the line-of-sight is intersecting a dynamically coherent structure in the CGM rather than a sea of orbiting clouds. The kinematic properties of the CGM are similar in the blue and red galaxies, although we find that a significantly larger fraction of the blue galaxies have large Lyman~$\alpha$ velocity offsets (>200 km s$^{-1}$). We show that - if the CGM clouds represent future fuel for star-formation - our new results could imply a large drop in the specific star-formation rate across the galaxy mass-range we probe.
The recent discovery of an enriched metallicity for the Smith high-velocity HI cloud (SC) lends support to a Galactic origin for this system. We use a dynamical model of the galactic fountain to reproduce the observed properties of the SC. In our model, fountain clouds are ejected from the region of the disc spiral arms and move through the halo interacting with a pre-existing hot corona. We find that a simple model where cold gas outflows vertically from the Perseus spiral arm reproduces the kinematics and the distance of the SC, but is in disagreement with the cloud's cometary morphology, if this is produced by ram-pressure stripping by the ambient gas. To explain the cloud morphology we explore two scenarios: a) the outflow is inclined with respect to the vertical direction; b) the cloud is entrained by a fast wind that escapes an underlying superbubble. Solutions in agreement with all observational constraints can be found for both cases, the former requires outflow angles >40 deg while the latter requires >1000 km/s winds. All scenarios predict that the SC is in the ascending phase of its trajectory and have large - but not implausible - energy requirements.
We present ALMA observations of the inner 1' (1.2 kpc) of the Circinus galaxy, the nearest Seyfert. We target CO (1-0) in the region associated with a well-known multiphase outflow driven by the central active galactic nucleus (AGN). While the geometry of Circinus and its outflow make disentangling the latter difficult, we see indications of outflowing molecular gas at velocities consistent with the ionized outflow. We constrain the mass of the outflowing molecular gas to be 1.5e5 -5.1e6 solar masses, yielding a molecular outflow rate of 0.35-12.3 solar masses per year. The values within this range are comparable to the star formation rate in Circinus, indicating that the outflow indeed regulates star formation to some degree. The molecular outflow in Circinus is considerably lower in mass and energetics than previously-studied AGN-driven outflows, especially given its high ratio of AGN luminosity to bolometric luminosity. The molecular outflow in Circinus is, however, consistent with some trends put forth in Cicone et al. (2014), including a linear relation between kinetic power and AGN luminosity, as well as its momentum rate vs. bolometric luminosity (although the latter places Circinus among the starburst galaxies in that sample). We detect additional molecular species including CN and C17O.
The absence of large cooling flows in cool core clusters appears to require self-regulated energy feedback by active galactic nuclei (AGNs) but the exact heating mechanism has not yet been identified. Here, we analyse whether a combination of cosmic ray (CR) heating and thermal conduction can offset radiative cooling. To this end, we compile a large sample of 39 cool core clusters and determine steady state solutions of the hydrodynamic equations that are coupled to the CR energy equation. We find stable solutions that match the observed density and temperature profiles for all our clusters well. Radiative cooling is balanced by CR heating in the cluster centres and by thermal conduction on larger scales, thus demonstrating the relevance of both heating mechanisms. Our mass deposition rates vary by three orders of magnitude and are linearly correlated to the observed star formation rates. Clusters with large mass deposition rates show larger cooling radii and require a larger radial extent of the CR injection function. Interestingly, our sample shows a continuous sequence in cooling properties: clusters hosting radio mini halos are characterised by the largest cooling radii, star formation and mass deposition rates in our sample and thus signal the presence of a higher cooling activity. The steady state solutions support the structural differences between clusters hosting a radio mini halo and those that do not.
Self-regulated feedback by active galactic nuclei (AGNs) appears to be critical in balancing radiative cooling of the low-entropy gas at the centres of galaxy clusters and in regulating star formation in central galaxies. In a companion paper, we found stable steady-state solutions of the hydrodynamic equations that are coupled to the CR energy equation for a large cluster sample. In those solutions, radiative cooling in the central region is balanced by streaming CRs through the generation and dissipation of resonantly generated Alfv{\'e}n waves and by thermal conduction at large radii. Here we demonstrate that the predicted non-thermal emission resulting from hadronic CR interactions in the intra-cluster medium exceeds observational radio (and gamma-ray) data in a subsample of clusters that host radio mini halos (RMHs). In contrast, the predicted non-thermal emission is well below observational data in cooling galaxy clusters without RMHs. These are characterised by exceptionally large AGN radio fluxes, indicating high CR yields and associated CR heating rates. We suggest a self-regulation cycle of AGN feedback in which non-RMH clusters are heated by streaming CRs homogeneously throughout the central cooling region. We predict {\em radio micro halos} surrounding the AGNs of these CR-heated clusters in which the primary emission may predominate the hadronically generated emission. Once the CR population has streamed sufficiently far and lost enough energy, the cooling rate increases, which explains the increased star formation rates in clusters hosting RMHs. Those could be powered hadronically by CRs that have previously heated the cluster core.
Recent analysis of strongly-lensed sources in the Hubble Frontier Fields indicates that the rest-frame UV luminosity function of galaxies at $z=$6--8 rises as a power law down to $M_\mathrm{UV}=-15$, and possibly as faint as -12.5. We use predictions from a cosmological radiation hydrodynamic simulation to map these luminosities onto physical space, constraining the minimum dark matter halo mass and stellar mass that the Frontier Fields probe. While previously-published theoretical studies have suggested or assumed that early star formation was suppressed in halos less massive than $10^9$--$10^{11} M_\odot$, we find that recent observations demand vigorous star formation in halos at least as massive as (3.1, 5.6, 10.5)$\times10^9 M_\odot$ at $z=(6,7,8)$. Likewise, we find that Frontier Fields observations probe down to stellar masses of (8.1, 18, 32)$\times10^6 M_\odot$; that is, they are observing the likely progenitors of analogues to Local Group dwarfs such as Pegasus and M32. Our simulations yield somewhat different constraints than two complementary models that have been invoked in similar analyses, emphasizing the need for further observational constraints on the galaxy-halo connection.
The Orion A molecular cloud is one of the most well-studied nearby star-forming regions, and includes regions of both highly clustered and more dispersed star formation across its full extent. Here, we analyze dense, star-forming cores identified in the 850 {\mu}m and 450 {\mu}m SCUBA-2 maps from the JCMT Gould Belt Legacy Survey. We identify dense cores in a uniform manner across the Orion A cloud and analyze their clustering properties. Using two independent lines of analysis, we find evidence that clusters of dense cores tend to be mass segregated, suggesting that stellar clusters may have some amount of primordial mass segregation already imprinted in them at an early stage. We also demonstrate that the dense core clusters have a tendency to be elongated, perhaps indicating a formation mechanism linked to the filamentary structure within molecular clouds.
Currently only a small number of Milky Way (MW) stars are known to exist beyond 100 kpc from the Galactic center. Though the distribution of these stars in the outer halo is believed to be sparse, they can provide evidence of more recent accretion events than in the inner halo and help map out the MW's dark matter halo to its virial radius. We have re-examined the outermost regions of 11 existing stellar halo models with two synthetic surveys: one mimicking present-day searches for distant M giants and another mimicking RR Lyrae (RRLe) projections for LSST. Our models suggest that color and proper motion cuts currently used to select M giant candidates for follow-up successfully remove nearly all halo dwarf self-contamination and are useful for focusing observations on distant M giants, of which there are thousands to tens of thousands beyond 100 kpc in our models. We likewise expect that LSST will identify comparable numbers of RRLe at these distances. We demonstrate that several observable properties of both tracers, such as proximity of neighboring stars, proper motions, and distances (for RRLe) could help us separate different accreted structures from one another. We also discuss prospects for using ratios of M giants to RRLe as a proxy for accretion time, which in the future could provide new constraints on the recent accretion history of our Galaxy.
We have performed a multi-wavelength analysis of a mid-infrared (MIR) bubble N37 and its surrounding environment. The selected 15$' \times$15$'$ area around the bubble contains two molecular clouds (N37 cloud; V$_{lsr}\sim$37-43 km s$^{-1}$, and C25.29+0.31; V$_{lsr}\sim$43-48 km s$^{-1}$) along the line of sight. A total of seven OB stars are identified towards the bubble N37 using photometric criteria, and two of them are spectroscopically confirmed as O9V and B0V stars. Spectro-photometric distances of these two sources confirm their physical association with the bubble. The O9V star is appeared to be the primary ionizing source of the region, which is also in agreement with the desired Lyman continuum flux analysis estimated from the 20 cm data. The presence of the expanding HII region is revealed in the N37 cloud which could be responsible for the MIR bubble. Using the $^{13}$CO line data and photometric data, several cold molecular condensations as well as clusters of young stellar objects (YSOs) are identified in the N37 cloud, revealing ongoing star formation (SF) activities. However, the analysis of ages of YSOs and the dynamical age of the HII region do not support the origin of SF due to the influence of OB stars. The position-velocity analysis of $^{13}$CO data reveals that two molecular clouds are inter-connected by a bridge-like structure, favoring the onset of a cloud-cloud collision process. The SF activities (i.e. the formation of YSOs clusters and OB stars) in the N37 cloud are possibly influenced by the cloud-cloud collision.
We present the stellar kinematic maps of a large sample of galaxies from the integral-field spectroscopic survey CALIFA. The sample comprises 300 galaxies displaying a wide range of morphologies across the Hubble sequence, from ellipticals to late-type spirals. This dataset allows us to homogeneously extract stellar kinematics up to several effective radii. In this paper, we describe the level of completeness of this subset of galaxies with respect to the full CALIFA sample, as well as the virtues and limitations of the kinematic extraction compared to other well-known integral-field surveys. In addition, we provide averaged integrated velocity dispersion radial profiles for different galaxy types, which are particularly useful to apply aperture corrections for single aperture measurements or poorly resolved stellar kinematics of high-redshift sources. The work presented in this paper sets the basis for the study of more general properties of galaxies that will be explored in subsequent papers of the survey.
Aims: To gain insight into the expected gas dynamics at the interface of the
Galactic bar and spiral arms in our own Milky Way galaxy, we examine as an
extragalactic counterpart the evidence for multiple distinct velocity
components in the cold, dense molecular gas populating a comparable region at
the end of the bar in the nearby galaxy NGC3627.
Methods: We assemble a high resolution view of molecular gas kinematics
traced by CO(2-1) emission and extract line-of-sight velocity profiles from
regions of high and low gas velocity dispersion.
Results: The high velocity dispersions arise with often double-peaked or
multiple line-profiles. We compare the centroids of the different velocity
components to expectations based on orbital dynamics in the presence of bar and
spiral potential perturbations. A model of the region as the interface of two
gas-populated orbits families supporting the bar and the independently rotating
spiral arms provides an overall good match to the data. An extent of the bar to
the corotation radius of the galaxy is favored.
Conclusions: Using NGC3627 as an extragalactic example, we expect situations
like this to favor strong star formation events such as observed in our own
Milky Way since gas can pile up at the crossings between the orbit families.
The relative motions of the material following these orbits is likely even more
important for the build up of high density in the region. The surface densities
in NGC3627 are also so high that shear at the bar end is unlikely to
significantly weaken the star formation activity. We speculate that scenarios
in which the bar and spiral rotate at two different pattern speeds may be the
most favorable for intense star formation at such interfaces.
Powerful radio galaxies are often associated with gas-rich galaxy mergers. These mergers may provide the fuel to trigger starburst and active galactic nuclear (AGN) activity. In this Research Note, we study the host galaxies of three seemingly young or re-started radio sources that drive fast outflows of cool neutral hydrogen (HI) gas, namely 3C 293, 3C 305 and 4C 12.50 (PKS 1345+12). Our aim is to link the feedback processes in the central kpc-scale region with new information on the distribution of stars and gas at scales of the galaxy. For this, we use deep optical V-band imaging of the host galaxies, complemented with HI emission-line observations to study their gaseous environments. We find prominent optical tidal features in all three radio galaxies, which confirm previous claims that 3C 293, 3C 305 and 4C 12.50 have been involved in a recent galaxy merger or interaction. Our data show the complex morphology of the host galaxies, and identify the companion galaxies that are likely involved in the merger or interaction. The radio sources appear to be (re-)triggered at a different stage of the merger; 4C 12.50 is a pre-coalescent and possibly multiple merger, 3C 293 is a post-coalescent merger that is undergoing a minor interaction with a close satellite galaxy, while 3C 305 appears to be shaped by an interaction with a gas-rich companion. For 3C 293 and 3C 305, we do not detect HI beyond the inner ~30-45 kpc region, which shows that the bulk of the cold gas is concentrated within the host-galaxy, rather than along the widespread tidal features.
The HI halo clouds of the Milky Way and in particular the intermediate-velocity clouds (IVCs) are thought to be connected to Galactic fountain processes. Observations of fountain clouds are important for understanding the role of matter recycling and accretion onto the Galactic disk and subsequent star formation. Here, we quantify the amount of molecular gas in the Galactic halo. We focus on the rare class of molecular IVCs (MIVCs) and search for new objects. The HI-FIR correlation is studied across the entire northern and southern Galactic hemispheres at Galactic latitudes $|b|>20^\circ$ in order to determine the amount and distribution of molecular gas in IVCs. We use the most recent large-scale HI and FIR data, the Effelsberg Bonn-HI Survey, the Parkes Galactic All-Sky Survey, and the Planck FIR surveys. We present a catalogue of 239 MIVC candidates on the northern and southern Galactic hemispheres. Among these candidates all previously known MIVCs are recovered except for a single one only. The frequency of candidates differs significantly between the northern and southern Galactic hemispheres and between negative and positive LSR velocities as well. In our approach we analyse the local Galactic environment. Extrapolating to the entire Galaxy, the global inflow of atomic and molecular IVC gas onto the Milky Way may account for the major fraction of the gaseous mass needed for sustaining the current Galactic star formation rate.
McGaugh et al. (2016) have used their extensive SPARC sample to update the well-known mass-discrepancy-acceleration relation (MDAR), which is one of the major predicted "MOND laws". This is not a newly discovered relation. Rather, it improves on the many previous studies of it, with more and better data. Like its precedents, it bears crucial ramifications for the observed dynamical anomalies in disc galaxies, and, in particular, on their resolution by the MOND paradigm. Their result, indeed, constitute a triumph for MOND. However, unlike previous analyses of the MDAR, McGaugh et al. have chosen to obfuscate the MOND roots of their analysis, and its connection with, and implications for, this paradigm. For example, the fitting formula they use, seemingly as a result of some unexplained inspiration, follows in its salient properties from the basic tenets of MOND, and has already been used in the past in several MOND analyses. No other possible origin for such a function is known. Given that this formula had already been shown to reproduce correctly the observed rotation curves from the baryon distribution (as a MOND effect), it must have been clear, a priory, that it should describe correctly the MDAR, which is but a summary of rotation curves. The present paper corrects these oversights -- bringing to light the deep connections with MOND, suppressed by McGaugh et al. It also gives due credit to previous works, and discusses some new, important, but less known, aspects of this MOND relation.
Using numerical models of star clusters spanning a wide range in stellar metallicities (Z) we study the effects of a parent cluster's metallicity on the masses of BBHs merging in the local universe (z<0.2). We connect BBH merger times (t_delay) obtained from models of a given metallicity to the corresponding merger redshifts using a distribution of formation epochs for clusters of that stellar metallicity derived based on the cosmological star formation rate and metallicity evolution. We find that the mass distributions for BBH mergers in z<0.2 can have significant overlap even when created in clusters of widely different stellar metallicities. This makes it hard to infer metallicity from the masses of individual merging BBHs. As the cluster metallicity decreases, the peaks and distributions for masses of its BBHs merging in z<0.2 move to higher values, but for Z/Z_sun<0.05 they become insensitive to the cluster metallicity. We compare the intrinsic mass distributions for BBHs merging in z<0.2 from our models with those observed. Masses of LVT151012 and GW151226 are similar to the peaks of the intrinsic mass distributions for models with Z/Z_sun=0.25 and 0.75, and are within 1 sigma for models with Z/Z_sun<0.25 and Z/Z_sun>0.5, respectively. GW150914 is more massive (beyond 1 sigma) than typical BBHs merging in z<0.2 even for the lowest metallicity clusters we consider, but is within 2 sigma of the intrinsic mass distributions from clusters with Z/Z_sun<0.05. Of course, accounting for aLIGO detectability would push the intrinsic distributions towards higher masses, hence the detection of merging BBHs as massive as GW150914 would be less rare. Since cluster dynamics typically increases BBH masses via exchange encounters relative to what could form in isolation, mergers of BBHs as massive as GW150914 in z<0.2 is likely intrinsically rare in general.
We present an analysis of the orientation effects in SDSS quasar composite spectra. In a previous work we have shown that the equivalent width EW of the [OIII] {\lambda}5008{\AA} line is a reliable indicator of the inclination of the accretion disk. Here, we have selected a sample of ~15,000 quasars from the SDSS 7th Data Release and divided it in sub-samples with different values of EW([OIII]). We find inclination effects both on broad and narrow quasars emission lines, among which an increasing broadening from low to high EW for the broad lines and a decreasing importance of the blue component for the narrow lines. These effects are naturally explained with a variation of source inclination from nearly face-on to edge-on, confirming the goodness of EW([OIII]) as an orientation indicator. Moreover, we suggest that orientation effects could explain, at least partially, the origin of the anticorrelation between [OIII] and FeII intensities, i.e. the well known Eigenvector 1.
We analyze the wavelength-dependent variability of a sample of
spectroscopically confirmed active galactic nuclei (AGN) selected from near-UV
($NUV$) variable sources in the GALEX Time Domain Survey that have a large
amplitude of optical variability (difference-flux S/N $>$ 3) in the Pan-STARRS1
Medium Deep Survey (PS1 MDS). By matching GALEX and PS1 epochs in 5 bands
($NUV$, $g_{P1}$, $r_{P1}$, $i_{P1}$, $z_{P1}$) in time, and taking their flux
difference, we create co-temporal difference-flux spectral energy distributions
($\Delta f$SEDs) using two chosen epochs for each of the 23 objects in our
sample on timescales of about a year.
We confirm the "bluer-when-brighter" trend reported in previous studies, and
measure a median spectral index of the $\Delta f$SEDs of $\alpha_{\lambda}$ =
2.1 that is consistent with an accretion disk spectrum. We further fit the
$\Delta f$SEDs of each source with a standard accretion disk model in which the
accretion rate changes from one epoch to the other. In our sample, 17 out of 23
($\sim$74 %) sources are well described by this variable accretion-rate disk
model, with a median average characteristic disk temperature $\bar{T}^*$ of
$1.2\times 10^5$~K that is consistent with the temperatures expected given the
distribution of accretion rates and black hole masses inferred for the sample.
Our analysis also shows that the variable accretion rate model is a better fit
to the $\Delta f$SEDs than a simple power law.
The mechanism behind the shaping of bipolar planetary nebulae is still poorly understood. Accurately tracing the molecule-rich equatorial regions of post-AGB stars can give valuable insight into the ejection mechanisms at work. We investigate the physical conditions, structure and velocity field of the dense molecular region of the planetary nebula NGC 6302 by means of ALMA band 7 interferometric maps. The high spatial resolution of the $^{12}$CO and $^{13}$CO J=3-2 ALMA data allows for an analysis of the geometry of the ejecta in unprecedented detail. We built a spatio-kinematical model of the molecular region with the software SHAPE and performed detailed non-LTE calculations of excitation and radiative transfer with the SHAPEMOL plug-in. We find that the molecular region consists of a massive ring out of which a system of fragments of lobe walls emerge and enclose the base of the lobes visible in the optical. The general properties of this region are in agreement with previous works, although the much greater spatial resolution of the data allows for a very detailed description. We confirm that the mass of the molecular region is 0.1 M$_{\odot}$. Additionally, we report a previously undetected component at the nebular equator, an inner, younger ring inclined $\sim$60$^\circ$ with respect to the main ring, showing a characteristic radius of 7.5$\times$10$^{16}$ cm, a mass of 2.7$\times$10$^{-3}$ M$_{\odot}$, and a counterpart in optical images of the nebula. This inner ring has the same kinematical age as the northwest optical lobes, implying it was ejected approximately at the same time, hundreds of years after the ejection of the bulk of the molecular ring-like region. We discuss a sequence of events leading to the formation of the molecular and optical nebulae, and briefly speculate on the origin of this intriguing inner ring.
We present the results of a search for HI 21-cm line emission from the
circumstellar environments of four Galactic Cepheids (RS Pup, X Cyg, $\zeta$
Gem, and T Mon) based on observations with the Karl G. Jansky Very Large Array.
The observations were aimed at detecting gas associated with previous or
ongoing mass loss. Near the long-period Cepheid T Mon, we report the detection
of a partial shell-like structure whose properties appear consistent with
originating from an earlier epoch of Cepheid mass loss. At the distance of T
Mon, the nebula would have a mass (HI+He) of $\sim0.5M_{\odot}$, or $\sim$6\%
of the stellar mass. Assuming that one-third of the nebular mass comprises
swept-up interstellar gas, we estimate an implied mass-loss rate of ${\dot
M}\sim (0.6-2)\times10^{-5} M_{\odot}$ yr$^{-1}$. No clear signatures of
circumstellar emission were found toward $\zeta$ Gem, RS Pup, or X Cyg,
although in each case, line-of-sight confusion compromised portions of the
spectral band. For the undetected stars, we derive model-dependent $3\sigma$
upper limits on the mass-loss rates, averaged over their lifetimes on the
instability strip, of $<(0.3-6)\times10^{-6} M_{\odot}$ yr$^{-1}$ and estimate
the total amount of mass lost to be less than a few per cent of the stellar
mass.
The Massive Young Star Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog (MIRES) and Chandra-based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1,109 MYStIX Candidate Protostars (MCPs) are found in 14 star forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few 'false positives' from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many 'false negatives'. Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be eludicated.
Context: Quantifying the gas content inside the dust gaps of transition disks is important to establish their origin. Aims: We seek to constrain the surface density of warm gas in the disk of HD 139614, a Herbig Ae star with a transition disk exhibiting a dust gap from 2.3 to 6 AU. Methods: We have obtained ESO/VLT CRIRES high-resolution spectra of CO ro-vibrational emission. We derive disk structure constraints by modeling the line profiles, the spectroastrometric signal, and the rotational diagrams using flat Keplerian disk models. Results: We detected v=1-0 12CO, 2-1 12CO, 1-0 13CO, 1-0 C18O, and 1-0 C17O ro-vibrational lines. 12CO v=1-0 lines have an average width of 14 km/s, Tgas of 450 K and an emitting region from 1 to 15 AU. 13CO and C18O lines are on average 70 and 100 K colder, 1 and 4 km/s narrower, and are dominated by emission at R>6 AU. The 12CO v=1-0 line profile indicates that if there is a gap in the gas it must be narrower than 2 AU. We find that a drop in the gas surface density (delta_gas) at R=5-6 AU is required to reproduce the line profiles and rotational diagrams of the three CO isotopologues simultaneously. Delta_gas can range from 10^-2 to 10^-4 depending on the outer disk's gas-to-dust ratio. We find that at 1<R<6 AU the gas surface density profile is flat or increases with radius. We derive a gas column density at 1<R<6 AU of NH=5x10^19 - 10^21 cm^-2. We find a 5sigma upper limit on NCO at R<1 AU of 5x10^15 cm^-2 (NH<5x10^19 cm^-2). Conclusions: The dust gap in the disk of HD 139614 has gas. The gas surface density in the disk at R<6 AU is significantly lower than the surface density expected from HD 139614's accretion rate assuming a viscous alpha-disk model. The gas density drop, the non-negative density gradient of the gas inside 6 AU, and the absence of a wide (>2 AU) gas gap suggest the presence of an embedded <2 MJ planet at around 4 AU.
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Cosmological simulations of galaxy formation can produce present-day galaxies with a large range of assembly and star formation histories. A detailed study of the metallicity evolution and star formation history of such simulations can assist in predicting LIGO-detectable compact object binary mergers. Recent simulations of compact binary evolution suggest the compact object merger rate depends sensitively on the progenitor's metallicity. Rare low-metallicity star formation during galaxy assembly can produce more detected compact binaries than typical star formation. Using detailed simulations of galaxy and chemical evolution, we determine how sensitively the compact binary populations of galaxies with similar present-day appearance depend on the details of their assembly. We also demonstrate by concrete example the extent to which dwarf galaxies overabundantly produce compact binary mergers, particularly binary black holes, relative to more massive galaxies. We discuss the implications for transient multimessenger astronomy with compact binary sources.
We present the first study of the isotropy of the distribution of morphological types of galaxies in the Local Universe out to around 200 Mpc using more than 60,000 galaxies from the HyperLeda database. We divide the sky into two opposite hemispheres and compare the abundance distribution of the morphological types, $T$, using the Kolmogorov-Smirnov (KS) test. This is repeated for different directions in the sky and the KS statistic as a function of sky coordinates is obtained. For three samples of galaxies within around 100, 150, and 200 Mpc, we find a significant hemispherical asymmetry with a vanishingly small chance of occurring in an isotropic distribution. Astonishingly, regardless of this extreme significance, the hemispherical asymmetry is aligned with the Celestial Equator at the 97.1-99.8% and with the Ecliptic at the 94.6-97.6% confidence levels, estimated using a Monte Carlo analysis. Shifting $T$ values randomly within their uncertainties has a negligible effect on this result. When a magnitude limit of $B\leq 15$ mag is applied, the sample within 100 Mpc shows no significant anisotropy after random shifting of $T$. However, the direction of the asymmetry in the samples within 150 and 200 Mpc and $B\leq 15$ mag is found to be within an angular separation of 32 degrees from $(l,b)=(123.7, 24.6)$ with 97.2% and 99.9% confidence levels, respectively. This direction is only 2.6 degrees away from the Celestial North Pole. Unless the Local Universe has a significant anisotropic distribution of galaxy types aligned with the orientation or the orbit of the Earth (which would be a challenge for the Cosmological Principle), our results show that there seems to be a systematic bias in the classification of galaxy morphological types between the data from the Northern and the Southern Equatorial sky. Further studies are absolutely needed to find out the exact source of this anisotropy.
Searching for active galactic nuclei (AGN) in dwarf galaxies is important for our understanding of the seed black holes that formed in the early Universe. Here, we test infrared selection methods for AGN activity at low galaxy masses. Our parent sample consists of ~18,000 nearby dwarf galaxies (M*< 3 x 10^9 Msun, $z<0.055$) in the Sloan Digital Sky Survey with significant detections in the first three bands of the AllWISE data release from the Wide-field Infrared Survey Explorer (WISE). First, we demonstrate that the majority of optically-selected AGNs in dwarf galaxies are not selected as AGNs using WISE infrared color diagnostics and that the infrared emission is dominated by the host galaxies. We then investigate the infrared properties of optically-selected star-forming dwarf galaxies, finding that the galaxies with the reddest infrared colors are the most compact, with blue optical colors, young stellar ages and large specific star formation rates. These results indicate that great care must be taken when selecting AGNs in dwarf galaxies using infrared colors, as star-forming dwarf galaxies are capable of heating dust in such a way that mimics the infrared colors of more luminous AGNs. In particular, a simple $\mathrm{W1}-\mathrm{W2}$ color cut alone should not be used to select AGNs in dwarf galaxies. With these complications in mind, we present a sample of 41 dwarf galaxies worthy of follow-up observations that fall in WISE infrared color space typically occupied by more luminous AGNs.
We compared the properties of 56 elliptical galaxies selected from three clusters at 1.2<z<1.4 with those of field galaxies at the same redshift in the GOODS-S (~30), COSMOS (~180) and CANDELS (~220) fields. We derived the relationships among effective radius, surface brightness, stellar mass, effective stellar mass density Sigma_Re and central mass density Sigma_1kpc within 1 kpc radius. We find that cluster elliptical galaxies do not differ from field ellipticals: they share the same structural parameters at fixed mass and the same scaling relations. On the other hand, the population of field ellipticals at z~1.3 shows a significant lack of massive (M*> 2x10^{11} Msun) and large (Re > 4-5 kpc) ellipticals with respect to the cluster. Nonetheless, at M*< 2x10^{11} Msun, the two populations are similar. The size-mass relation of cluster and field ellipticals at z~1.3 defines two different regimes, above and below a transition mass m_t~2-3x10^{10} Msun: at lower masses the relation is nearly flat (Re\propto M*^{-0.1\pm0.2}), the mean radius is constant at ~1 kpc and, consequenly, Sigma_Re ~ Sigma_1kpc while, at larger masses, the relation is Re\propto M*^{0.64\pm0.09}. The transition mass marks the mass at which galaxies reach the maximum Sigma_Re. Also the Sigma_1kpc-mass relation follows two different regimes, above and below m_t, (Sigma_1kpc\propto M*^{0.64\ >m_t}_{1.07\ <m_t}) defining a transition mass density Sigma_1kpc~2-3x10^3 Msun pc^{-2}. The effective stellar mass density Sigma_Re does not correlate with mass, dense/compact galaxies can be assembled over a wide mass regime, independently of the environment. The central stellar mass density, Sigma_1kpc, besides to be correlated with the mass, is correlated to the age of the stellar population: the higher the central stellar mass density, the higher the mass, the older the age of the stellar population. [Abridged]
We use the high-resolution cosmological simulation Illustris to investigate the clustering of supermassive black holes across cosmic time, the link between black hole clustering and host halo masses, and the implications for black hole duty cycles. Our predicted black hole correlation length and bias match the observational data very well across the full redshift range probed. Black hole clustering is strongly luminosity-dependent on small, 1-halo scales, with some moderate dependence on larger scales of a few Mpc at intermediate redshifts. We find black hole clustering to evolve only weakly with redshift, initially following the behaviour of their hosts. However below z ~ 2 black hole clustering increases faster than that of their hosts, which leads to a significant overestimate of the clustering-predicted host halo mass. The full distribution of host halo masses is very wide, including a low-mass tail extending up to an order of magnitude below the naive prediction for minimum host mass. Our black hole duty cycles follow a power-law dependence on black hole mass and decrease with redshift, and we provide accurate analytic fits to these. The increase in clustering amplitude at late times, however, means that duty cycle estimates based on black hole clustering can overestimate duty cycles substantially, by more than two orders of magnitude. We find the best agreement when the minimum host mass is assumed to be $10^{11.2} M_\odot$ , which provides an accurate measure across all redshifts and luminosity ranges probed by our simulation.
We report the second complete molecular line data release from the {\em Census of High- and Medium-mass Protostars} (CHaMP), a large-scale, unbiased, uniform mapping survey at sub-parsec resolution, of mm-wave line emission from 303 massive, dense molecular clumps in the Milky Way. This release is for all $^{12}$CO $J$=1$\rightarrow$0 emission associated with the dense gas, the first from Phase II of the survey, which includes $^{12}$CO, $^{13}$CO, and C$^{18}$O. The observed clump emission traced by both $^{12}$CO and HCO$^+$ (from Phase I) shows very similar morphology, indicating that, for dense molecular clouds and complexes of all sizes, parsec-scale clumps contain $\Xi$ ~ 75% of the mass, while only 25% of the mass lies in extended (>~ 10 pc) or "low density" components in these same areas. The mass fraction of all gas above a density 10$^9$ m$^{-3}$ is $\xi_9$ >~ 50%. This suggests that parsec-scale clumps may be the basic building blocks of the molecular ISM, rather than the standard GMC concept. Using $^{12}$CO emission, we derive physical properties of these clumps in their entirety, and compare them to properties from HCO$^+$, tracing their denser interiors. We compare the standard X-factor converting $I_{CO}$ to $N_{H_2}$ with alternative conversions, and show that only the latter give whole-clump properties that are physically consistent with those of their interiors. We infer that the clump population is systematically closer to virial equilibrium than when considering only their interiors, with perhaps half being long-lived (10s of Myr), pressure-confined entities which only terminally engage in vigorous massive star formation, supporting other evidence along these lines previously published.
We use the Low Frequency Array to perform a systematic high spectral
resolution investigation of the low-frequency 33-78 MHz spectrum along the line
of sight to Cassiopeia A. We complement this with a 304-386 MHz Westerbork
Synthesis Radio telescope observation. In this first paper we focus on the
carbon radio recombination lines.
We detect Cn$\alpha$ lines at -47 and -38 km s$^{-1}$ in absorption for
quantum numbers n=438-584 and in emission for n=257-278 with high signal to
noise. These lines are associated with cold clouds in the Perseus spiral arm
component. Hn$\alpha$ lines are detected in emission for n=257-278. In
addition, we also detect Cn$\alpha$ lines at 0 km s$^{-1}$ associated with the
Orion arm.
We analyze the optical depth of these transitions and their line width. Our
models show that the carbon line components in the Perseus arm are best fit
with an electron temperature 85 K and an electron density 0.04 cm$^{-3}$ and
can be constrained to within 15\%. The electron pressure is constrained to
within 20\%. We argue that much of these carbon radio recombination lines arise
in the CO-dark surface layers of molecular clouds where most of the carbon is
ionized but hydrogen has made the transition from atomic to molecular. The
hydrogen lines are clearly associated with the carbon line emitting clouds, but
the low-frequency upperlimits indicate that they likely do not trace the same
gas. Combining the hydrogen and carbon results we arrive at a firm lower limit
to the cosmic ray ionization rate of 2.5$\times$10$^{-18}$ s$^{-1}$.
We numerically reproduce the density profiles for filaments that are in
magnetohydrostatic and pressure equilibrium with their surroundings obtained in
Tomisaka (2014) and show that these equilibria are dynamically stable. If the
effect of ambipolar diffusion is considered, these filaments lose magnetic
support initiating cloud collapse. The filaments do not lose magnetic flux.
Rather the magnetic flux is redistributed within the filament from the centre
towards the envelope.
The rate of the collapse is inversely proportional to the fractional
ionisation and two gravitationally-driven ambipolar diffusion regimes for the
collapse are observed as predicted in Mouschovias & Morton (1991). For high
values of the ionisation coefficient, that is $X \geq 10^{-7}$, the gas is
strongly coupled to the magnetic field and the Jeans length is larger than the
ambipolar diffusion length scale. Then the collapse is governed by
magnetically-regulated ambipolar diffusion. For $X \lesssim 10^{-8}$, the gas
is weakly coupled to the magnetic field and the magnetic support is removed by
gravitationally-dominated ambipolar diffusion. Here, neutrals and ions only
collide sporadically, that is the ambipolar diffusion length scale is larger
than the Jeans length.
When decaying turbulence is included, additional support is provided to the
filament. This slows down the collapse of the filament even in the absence of a
magnetic field. When a magnetic field is present, the collapse rate increases
by a ratio smaller than for the non-magnetic case. This is because of a
speed-up of the ambipolar diffusion due to larger magnetic field gradients
generated by the turbulence and because the ambipolar diffusion aids the
dissipation of turbulence below the ambipolar diffusion length scale. The
highest increase in the rate is observed for the lowest ionisation coefficient
and the highest turbulent intensity.
We use the concept of the spiral rotation curves universality (see Parsic et
al. 1996) to investigate the luminous and dark matter properties of the dwarf
disk galaxies in the local volume (size $\sim11$ Mpc). Our sample includes 36
objects with rotation curves carefully selected from the literature. We find
that, despite the large variations of our sample in luminosities ($\sim$ 2 of
dex), the rotation curves in specifically normalized units, look all alike and
lead to the lower-mass version of the universal rotation curve of spiral
galaxies found in Parsic et al. 1996.
We mass model $V(R/R_{opt})/V_{opt}$, the double normalized universal
rotation curve of dwarf disk galaxies: the results show that these systems are
totally dominated by dark matter whose density shows a core size between 2 and
3 stellar disk scale lengths. Similar to galaxies of different Hubble types and
luminosities, the core radius $r_0$ and the central density $\rho_0$ of the
dark matter halo of these objects are related by $ \rho_0 r_0 \sim 100 M_\odot
pc^{-2}$.
The structural properties of the dark and luminous matter emerge very well
correlated. In addition, to describe these relations, we need to introduce a
new parameter, measuring the compactness of light distribution of a (dwarf)
disk galaxy. These structural properties also indicate that there is no
evidence of abrupt decline at the faint end of the baryonic to halo mass
relation. Finally, we find that the distributions of the stellar disk and its
dark matter halo are closely related.
The original ALHAMBRA catalogue contained over 400,000 galaxies selected using a synthetic F814W image, to the magnitude limit AB(F814W)$\approx$24.5. Given the photometric redshift depth of the ALHAMBRA multiband data (<z>=0.86) and the approximately $I$-band selection, there is a noticeable bias against red objects at moderate redshift. We avoid this bias by creating a new catalogue selected in the $K_s$ band. This newly obtained catalogue is certainly shallower in terms of apparent magnitude, but deeper in terms of redshift, with a significant population of red objects at $z>1$. We select objects using the $K_s$ band images, which reach an approximate AB magnitude limit $K_s \approx 22$. We generate masks and derive completeness functions to characterize the sample. We have tested the quality of the photometry and photometric redshifts using both internal and external checks. Our final catalogue includes $\approx 95,000$ sources down to $K_s \approx 22$, with a significant tail towards high redshift. We have checked that there is a large sample of objects with spectral energy distributions that correspond to that of massive, passively evolving galaxies at $z > 1$, reaching as far as $z \approx 2.5$. We have tested the possibility of combining our data with deep infrared observations at longer wavelengths, particularly Spitzer IRAC data.
We explore the parameter space of the semi-analytic galaxy formation model GALFORM, studying the constraints imposed by measurements of the galaxy stellar mass function (GSMF) and its evolution. We use the Bayesian Emulator method to quickly eliminate vast implausible volumes of the parameter space and zoom in on the most interesting regions, allowing us to identify a set of models that match the observational data within the model uncertainties. We find that the GSMF strongly constrains parameters related to the quiescent star formation in discs, stellar and AGN feedback and the threshold for disc instabilities, but more weakly restricts other parameters. Constraining the model using the local data alone does not usually select models that match the evolution of the mass function well. Nevertheless, we show that a small subset of models provides an acceptable match to GSMF data out to redshift 1.5, without introducing an explicit redshift dependence of feedback parameters. We explore the physical significance of the parameters of these models, in particular exploring whether the model can provide a better description if the mass loading of the galactic winds generated by starbursts ($\beta_{0,\text{burst}}$) and quiescent disks ($\beta_{0,\text{disc}}$) is different. Performing a principal component analysis of the plausible volume of the parameter space, we write a set of relations between parameters obeyed by plausible models with respect to the GSMF evolution. We find that while $\beta_{0,\text{disc}}$ is strongly constrained by GSMF evolution data, constraints on $\beta_{0,\text{burst}}$ are weak. We discuss the implications of these results.
In the first paper of this series, we study the level population problem of recombining carbon ions. We focus our study on high quantum numbers anticipating observations of Carbon Radio Recombination Lines to be carried out by the LOw Frequency ARray (LOFAR). We solve the level population equation including angular momentum levels with updated collision rates up to high principal quantum numbers. We derive departure coefficients by solving the level population equation in the hydrogenic approximation and including low temperature dielectronic recombination effects. Our results in the hydrogenic approximation agree well with those of previous works. When comparing our results including dielectronic recombination we find differences which we ascribe to updates in the atomic physics (e.g., collision rates) and to the approximate solution method of the statistical equilibrium equations adopted in previous studies. A comparison with observations is discussed in an accompanying article, as radiative transfer effects need to be considered.
In recent work done by Sun et. al., the color variation of quasars, namely the bluer-when-brighter trend, was found to be timescale-dependent using SDSS $g/r$ band light curves in the Stripe 82. Such timescale dependence, i.e., bluer variation at shorter timescales, supports the thermal fluctuation origin of the UV/optical variation in quasars, and can be well modeled with the inhomogeneous accretion disk model. In this paper, we extend the study to much shorter wavelengths in the rest frame (down to extreme UV), using GALaxy Evolution eXplorer (GALEX) photometric data of quasars collected in two ultraviolet bands (near-UV and far-UV). We develop Monte-Carlo simulations to correct possible biases due to the considerably larger photometric uncertainties in GALEX light curves (particularly in far-UV, comparing with SDSS $g/r$ bands), which otherwise could produce artificial results. We securely confirm the previously discovered timescale dependence of the color variability with independent datasets and at shorter wavelengths. We further find the slope of the correlation between the amplitude of color variation and timescale however appears even steeper than that predicted by the inhomogeneous disk model, which assumes that disk fluctuations follow damped random walk process. In line with the much flatter structure function observed in far-UV comparing with that at longer wavelengths, this implies deviation from DRW process in the inner disk where rest frame extreme UV radiation is produced.
We present a study on galaxy detection and shape classification using topometric clustering algorithms. We first use the DBSCAN algorithm to extract, from CCD frames, groups of adjacent pixels with significant fluxes and we then apply the DENCLUE algorithm to separate the contributions of overlapping sources. The DENCLUE separation is based on the localization of pattern of local maxima, through an iterative algorithm which associates each pixel to the closest local maximum. Our main classification goal is to take apart elliptical from spiral galaxies. We introduce new sets of features derived from the computation of geometrical invariant moments of the pixel group shape and from the statistics of the spatial distribution of the DENCLUE local maxima patterns. Ellipticals are characterized by a single group of local maxima, related to the galaxy core, while spiral galaxies have additional ones related to segments of spiral arms. We use two different supervised ensemble classification algorithms, Random Forest, and Gradient Boosting. Using a sample of ~ 24000 galaxies taken from the Galaxy Zoo 2 main sample with spectroscopic redshifts, and we test our classification against the Galaxy Zoo 2 catalog. We find that features extracted from our pipeline give on average an accuracy of ~ 93%, when testing on a test set with a size of 20% of our full data set, with features deriving from the angular distribution of density attractor ranking at the top of the discrimination power.
Abell 2146 consists of two galaxy clusters that have recently collided close to the plane of the sky, and it is unique in showing two large shocks on $\textit{Chandra X-ray Observatory}$ images. With an early stage merger, shortly after first core passage, one would expect the cluster galaxies and the dark matter to be leading the X-ray emitting plasma. In this regard, the cluster Abell 2146-A is very unusual in that the X-ray cool core appears to lead, rather than lag, the Brightest Cluster Galaxy (BCG) in their trajectories. Here we present a strong lensing analysis of multiple image systems identified on $\textit{Hubble Space Telescope}$ images. In particular, we focus on the distribution of mass in Abell 2146-A in order to determine the centroid of the dark matter halo. We use object colours and morphologies to identify multiple image systems; very conservatively, four of these systems are used as constraints on a lens mass model. We find that the centroid of the dark matter halo, constrained using the strongly lensed features, is coincident with the BCG, with an offset of $\approx$ 2 kpc between the centres of the dark matter halo and the BCG. Thus from the strong lensing model, the X-ray cool core also leads the centroid of the dark matter in Abell 2146-A, with an offset of $\approx$ 30 kpc.
We present a multi-wavelength temporal analysis of the blazar 3C 454.3 during the high $\gamma$-ray active period from May-December, 2014. Except for X-rays, the period is well sampled at near-infrared (NIR)-optical by the \emph{SMARTS} facility and the source is detected continuously on daily timescale in the \emph{Fermi}-LAT $\gamma$-ray band. The source exhibits diverse levels of variability with many flaring/active states in the continuously sampled $\gamma$-ray light curve which are also reflected in the NIR-optical light curves and the sparsely sampled X-ray light curve by the \emph{Swift}-XRT. Multi-band correlation analysis of this continuous segment during different activity periods shows a change of state from no lags between IR and $\gamma$-ray, optical and $\gamma$-ray, and IR and optical to a state where $\gamma$-ray lags the IR/optical by $\sim$3 days. The results are consistent with the previous studies of the same during various $\gamma$-ray flaring and active episodes of the source. This consistency, in turn, suggests an extended localized emission region with almost similar conditions during various $\gamma$-ray activity states. On the other hand, the delay of $\gamma$-ray with respect to IR/optical and a trend similar to IR/optical in X-rays along with strong broadband correlations favor magnetic field related origin with X-ray and $\gamma$-ray being inverse Comptonized of IR/optical photons and external radiation field, respectively.
The rate at which matter flows into a galactic nucleus during early phases of galaxy evolution can sometimes exceed the Eddington limit of the growing central black hole by several orders of magnitude. We discuss the necessary conditions for the black hole to actually accrete this matter at such a high rate, and consider the observational appearance and detectability of a hyperaccreting black hole. In order to be accreted at a hyper-Eddington rate, the infalling gas must have a sufficiently low angular momentum. Although most of the gas is accreted, a significant fraction accumulates in an optically thick envelope with luminosity $\sim L_{\rm Edd}$, probably pierced by jets of much higher power. If $\dot M > 10^3 \dot M_{\rm Edd}$, the envelope spectrum resembles a blackbody with a temperature of a few thousand K, but for lower (but still hyper-Eddington) accretion rates the spectrum becomes a very dilute and hard Wien spectrum. We consider the likelihood of various regimes of hyperaccretion, and discuss its possible observational signatures.
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