Abstract
Building on the first paper in this series (Duncan et al. 2018), we present a study investigating the performance of Gaussian process photometric redshift (photo-z) estimates for galaxies ...and active galactic nuclei (AGNs) detected in deep radio continuum surveys. A Gaussian process redshift code is used to produce photo-z estimates targeting specific subsets of both the AGN population – infrared (IR), X-ray, and optically selected AGNs – and the general galaxy population. The new estimates for the AGN population are found to perform significantly better at z > 1 than the template-based photo-z estimates presented in our previous study. Our new photo-z estimates are then combined with template estimates through hierarchical Bayesian combination to produce a hybrid consensus estimate that outperforms both of the individual methods across all source types. Photo-z estimates for radio sources that are X-ray sources or optical/IR AGNs are significantly improved in comparison to previous template-only estimates – with outlier fractions and robust scatter reduced by up to a factor of ∼4. The ability of our method to combine the strengths of the two input photo-z techniques and the large improvements we observe illustrate its potential for enabling future exploitation of deep radio continuum surveys for both the study of galaxy and black hole coevolution and for cosmological studies.
We look for correlated changes in stellar mass and star formation rate (SFR) along filaments in the cosmic web by examining the stellar masses and UV-derived SFRs of 1799 ungrouped and unpaired ...spiral galaxies that reside in filaments. We devise multiple distance metrics to characterize the complex geometry of filaments, and find that galaxies closer to the cylindrical centre of a filament have higher stellar masses than their counterparts near the periphery of filaments, on the edges of voids. In addition, these peripheral spiral galaxies have higher SFRs at a given mass. Complementing our sample of filament spiral galaxies with spiral galaxies in tendrils and voids, we find that the average SFR of these objects in different large-scale environments are similar to each other with the primary discriminant in SFR being stellar mass, in line with previous works. However, the distributions of SFRs are found to vary with large-scale environment. Our results thus suggest a model in which in addition to stellar mass as the primary discriminant, the large-scale environment is imprinted in the SFR as a second-order effect. Furthermore, our detailed results for filament galaxies suggest a model in which gas accretion from voids on to filaments is primarily in an orthogonal direction. Overall, we find our results to be in line with theoretical expectations of the thermodynamic properties of the intergalactic medium in different large-scale environments.
We present calibrations for star formation rate (SFR) indicators in the ultraviolet, mid-infrared, and radio-continuum bands, including one of the first direct calibrations of 150 MHz as an SFR ...indicator. Our calibrations utilize 66 nearby star-forming galaxies with Balmer-decrement-corrected luminosities, which span five orders of magnitude in SFR and have absolute magnitudes of . Most of our photometry and spectrophotometry are measured from the same region of each galaxy, and our spectrophotometry has been validated with SDSS photometry, so our random and systematic errors are small relative to the intrinsic scatter seen in SFR indicator calibrations. We find that the Wide-field Infrared Space Explorer W4 (22.8 m), Spitzer 24 m, and 1.4 GHz bands have tight correlations with the Balmer-decrement-corrected H luminosity, with a scatter of only 0.2 dex. Our calibrations are comparable to those from the prior literature for L∗ galaxies, but for dwarf galaxies, our calibrations can give SFRs that are far greater than those derived from most previous literature.
We have measured the relationships between H i mass, stellar mass, and star formation rate using the Hi Parkes All-Sky Survey Catalog (HICAT) and the Wide-field Infrared Survey Explorer (WISE). Of ...the 3513 HICAT sources, we find 3.4 m counterparts for 2896 sources (80%), and provide new WISE-matched aperture photometry for these galaxies. For our principal sample of spiral galaxies with W1 ≤ 10 mag and z ≤ 0.01, we identify H i detections for 93% of the sample. We measure lower H i-stellar mass relationships for H i-selected samples that do not include spiral galaxies with little H i gas. Our observations of the spiral sample show that H i mass increases with stellar mass with a power-law index of 0.35; however, this value is dependent on T-type, which affects both the median and the dispersion of Hi mass. We also observe an upper limit on the H i gas fraction, which is consistent with a halo spin parameter model. We measure the star formation efficiency of spiral galaxies to be constant at 10−9.57 yr−1 0.4 dex for 2.5 orders of magnitude in stellar mass, despite the higher stellar mass spiral showing evidence of quenched star formation.
We present radio active galactic nuclei (AGN) luminosity functions over the redshift range 0.005 < z < 0.75. The sample from which the luminosity functions are constructed is an optical spectroscopic ...survey of radio galaxies, identified from matched Faint Images of the Radio Sky at Twenty-cm survey (FIRST) sources and Sloan Digital Sky Survey images. The radio AGN are separated into low-excitation radio galaxies (LERGs) and high-excitation radio galaxies (HERGs) using the optical spectra. We derive radio luminosity functions for LERGs and HERGs separately in the three redshift bins (0.005 < z < 0.3, 0.3 < z < 0.5 and 0.5 < z < 0.75). The radio luminosity functions can be well described by a double power law. Assuming this double power-law shape the LERG population displays little or no evolution over this redshift range evolving as
${\sim } (1+z)^{0.06^{+0.17}_{-0.18}}$
assuming pure density evolution or
${\sim } (1+z)^{0.46^{+0.22}_{-0.24}}$
assuming pure luminosity evolution. In contrast, the HERG population evolves more rapidly, best fitted by
${\sim } (1+z)^{2.93^{+0.46}_{-0.47}}$
assuming a double power-law shape and pure density evolution. If a pure luminosity model is assumed, the best-fitting HERG evolution is parametrized by
${\sim } (1+z)^{7.41^{+0.79}_{-1.33}}$
. The characteristic break in the radio luminosity function occurs at a significantly higher power (≳1 dex) for the HERG population in comparison to the LERGs. This is consistent with the two populations representing fundamentally different accretion modes.
We present an atlas of 129 spectral energy distributions for nearby galaxies, with wavelength coverage spanning from the ultraviolet to the mid-infrared. Our atlas spans a broad range of galaxy ...types, including ellipticals, spirals, merging galaxies, blue compact dwarfs, and luminous infrared galaxies. We have combined ground-based optical drift-scan spectrophotometry with infrared spectroscopy from Spitzer and Akari with gaps in spectral coverage being filled using Multi-wavelength Analysis of Galaxy Physical Properties spectral energy distribution models. The spectroscopy and models were normalized, constrained, and verified with matched-aperture photometry measured from Swift, Galaxy Evolution Explorer, Sloan Digital Sky Survey, Two Micron All Sky Survey, Spitzer, and Wide-field Infrared Space Explorer images. The availability of 26 photometric bands allowed us to identify and mitigate systematic errors present in the data. Comparison of our spectral energy distributions with other template libraries and the observed colors of galaxies indicates that we have smaller systematic errors than existing atlases, while spanning a broader range of galaxy types. Relative to the prior literature, our atlas will provide improved K-corrections, photometric redshifts, and star-formation rate calibrations.
Multiple mechanisms quench passive spiral galaxies Fraser-McKelvie, Amelia; Brown, Michael J. I; Pimbblet, Kevin ...
Monthly notices of the Royal Astronomical Society,
02/2018, Letnik:
474, Številka:
2
Journal Article
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Abstract
We examine the properties of a sample of 35 nearby passive spiral galaxies in order to determine their dominant quenching mechanism(s). All five low-mass (M⋆ < 1 × 1010 M⊙) passive spiral ...galaxies are located in the rich Virgo cluster. This is in contrast to low-mass spiral galaxies with star formation, which inhabit a range of environments. We postulate that cluster-scale gas stripping and heating mechanisms operating only in rich clusters are required to quench low-mass passive spirals, and ram-pressure stripping and strangulation are obvious candidates. For higher mass passive spirals, while trends are present, the story is less clear. The passive spiral bar fraction is high: 74 ± 15 per cent, compared with 36 ± 5 per cent for a mass, redshift and T-type matched comparison sample of star-forming spiral galaxies. The high mass passive spirals occur mostly, but not exclusively, in groups, and can be central or satellite galaxies. The passive spiral group fraction of 74 ± 15 per cent is similar to that of the comparison sample of star-forming galaxies at 61 ± 7 per cent. We find evidence for both quenching via internal structure and environment in our passive spiral sample, though some galaxies have evidence of neither. From this, we conclude no one mechanism is responsible for quenching star formation in passive spiral galaxies – rather, a mixture of mechanisms is required to produce the passive spiral distribution we see today.
We have identified 335 galaxy cluster and group candidates, 106 of which are at image, using a 4.5 mum-selected sample of objects from a 7.25 deg super(2) region in the Spitzer Infrared Array Camera ...(IRAC) Shallow Survey. Clusters were identified as three-dimensional overdensities using a wavelet algorithm, based on photometric redshift probability distributions derived from IRAC and NOAO Deep Wide-Field Survey data. We estimate only image10% of the detections are spurious. To date 12 of the image candidates have been confirmed spectroscopically, at redshifts from 1.06 to 1.41. Velocity dispersions of image750 km s super(-1) for two of these argue for total cluster masses well above 10 super(14) M sub(image), as does the mass estimated from the rest-frame near-infrared stellar luminosity. Although not selected to contain a red sequence, some evidence for red sequences is present in the spectroscopically confirmed clusters, and brighter galaxies are systematically redder than the mean galaxy color in clusters at all redshifts. The mean image color for cluster galaxies up to image is well matched by a passively evolving model in which stars are formed in a 0.1 Gyr burst starting at redshift image. At image, a wider range of formation histories is needed, but higher formation redshifts (i.e., image) are favored for most clusters.
The Spitzer Space Telescope has revealed a significant population of high-redshift dust-obscured galaxies with large mid-infrared to ultraviolet luminosity ratios. Due to their optical faintness, ...these galaxies have been previously missed in traditional optical studies of the distant universe. We present a simple method for selecting this high-redshift population based solely on the ratio of the observed mid-infrared 24 mum to optical R- band flux density. We apply this method to observations of the sim8.6 deg super(2) NOAO Deep Wide-Field Survey Booetes field, and uncover sim2600 dust-obscured galaxy candidates i.e., 0.089 arcmin super(-2)) with 24 mum flux densities image mJy and image (i.e., image . These galaxies have no counterparts in the local universe. They represent image of the 24 mum source population at image mJy but increase to simimage of the population at sim0.3 mJy. These galaxies exhibit evidence of both star formation and AGN activity, with the brighter 24 mum sources being more AGN-dominated. We have measured spectroscopic redshifts for 86 of these galaxies, and find a broad redshift distribution centered at image. The space density of this population is image, similar to that of bright submillimeter-selected galaxies at comparable redshifts. These redshifts imply large luminosities, with median image L sub(image). The infrared luminosity density contributed by this relatively rare dust-obscured galaxy population is image. This is simimage % of that contributed by image ultraluminous infrared galaxies (ULIRGs, with image L sub(image)); our simple selection thus identifies a significant fraction of image ULIRGs. This IRLD is simimage of the total contributed by all image galaxies. We suggest that these dust-obscured galaxies are the progenitors of luminous (image4L*) present-day galaxies, seen undergoing an extremely luminous, short-lived phase of both bulge and black hole growth. They may represent a brief evolutionary phase between submillimeter-selected galaxies and less obscured quasars or galaxies.
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