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.
ABSTRACT We calibrate the integrated luminosity from the polycyclic aromatic hydrocarbon (PAH) features at 6.2, 7.7, and 11.3 m in galaxies as a measure of the star formation rate (SFR). These ...features are strong (containing as much as 5%-10% of the total infrared luminosity) and suffer minimal extinction. Our calibration uses Spitzer Infrared Spectrograph (IRS) measurements of 105 galaxies at 0 < z < 0.4, infrared (IR) luminosities of 109-1012 , combined with other well-calibrated SFR indicators. The PAH luminosity correlates linearly with the SFR as measured by the extinction-corrected H luminosity over the range of luminosities in our calibration sample. The scatter is 0.14 dex, comparable to that between SFRs derived from the Pa and extinction-corrected H emission lines, implying that the PAH features may be as accurate an SFR indicator as hydrogen recombination lines. The PAH SFR relation depends on gas-phase metallicity, for which we supply an empirical correction for galaxies with 0.2 < Z 0.7 . We present a case study in advance of the James Webb Space Telescope (JWST), which will be capable of measuring SFRs from PAHs in distant galaxies at the peak of the SFR density in the universe (z ∼ 2) with SFRs as low as ∼10 . We use Spitzer/IRS observations of the PAH features and Pa emission plus H measurements in lensed star-forming galaxies at 1 < z < 3 to demonstrate the ability of the PAHs to derive accurate SFRs. We also demonstrate that because the PAH features dominate the mid-IR fluxes, broadband mid-IR photometric measurements from JWST will both trace the SFR and provide a way to exclude galaxies dominated by an active galactic nucleus.
We have traced the past 7 Gyr of red galaxy stellar mass growth within dark matter halos. We have determined the halo occupation distribution, which describes how galaxies reside within dark matter ...halos, using the observed luminosity function and clustering of 40,696 image red galaxies in Booetes. Half of image10 super(11.9) h super(-1) M sub(image) halos host a red central galaxy, and this fraction increases with increasing halo mass. We do not observe any evolution of the relationship between red galaxy stellar mass and host halo mass, although we expect both galaxy stellar masses and halo masses to evolve over cosmic time. We find that the stellar mass contained within the red population has doubled since image, with the stellar mass within red satellite galaxies tripling over this redshift range. In cluster mass halos (>10 super(14) h super(-1) M sub(image)) most of the stellar mass resides within satellite galaxies and the intracluster light, with a minority of the stellar mass residing within central galaxies. The stellar masses of the most luminous red central galaxies are proportional to halo mass to the power of image0.35. We thus conclude that halo mergers do not always lead to rapid growth of central galaxies. While very massive halos often double in mass over the past 7 Gyr, the stellar masses of their central galaxies typically grow by only image30%.
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, Volume:
474, Issue:
2
Journal Article
Peer reviewed
Open access
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.
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