The many assembly histories of massive void galaxies as revealed by integral field spectroscopy

We present the first detailed integral field spectroscopy study of nine central void galaxies with M*>10¹⁰Mʘ using the Wide Field Spectrograph to determine how a range of assembly histories manifest themselves in the current day Universe.While the majority of these galaxies are evolving secularly, we find a range of morphologies, merger histories and stellar population distributions, though similarly low Hα-derived star formation rates (10¹⁰Mʘ have similarly low star formation rates

Evolution of the stellar mass function and infrared luminosity function of galaxies since z = 1.2

© 2019. The American Astronomical Society. All rights reserved. We measured evolution of the K-band luminosity function and stellar mass function (SMF) for red and blue galaxies at z 0.4 luminosity and mass function measurements. Using an evolving relation for K-band mass-to-light ratios as a function of (B-V) color, we found a slowly decreasing rate of growth in red galaxy stellar mass density of ×2.3 from z ∼ 1.1 to z ∼ 0.3, indicating a slowly decreasing rate of migration from the blue cloud to the red sequence. Unlike some studies of the SMF, we find that massive red galaxies grow by a factor of ×1.7 from z ∼ 1.1 to z ∼ 0.3, with the rate of growth due to mergers decreasing with time. These results are comparable with measurements of merger rates and clustering, and they are also consistent with the red galaxy stellar mass growth implied by comparing K-band luminosity evolution with the fading of passive stellar population models

MACHO 311.37557.169: A VY Scl star

Optical surveys, such as theMACHO project, often uncover variable stars whose classification requires follow-up observations by other instruments. We performed X-ray spectroscopy and photometry of the unusual variable starMACHO 311.37557.169 with XMM-Newton in April 2018, supplemented by archival X-ray and optical spectrographic data. The star has a bolometric X-ray luminosity of about 1 × 1032 erg s−1 cm−2 and a heavily absorbed two-temperature plasma spectrum. The shape of its light curve, its overall brightness, its X-ray spectrum, and the emission lines in its optical spectrum suggest that it is most likely a VY Scl cataclysmic variable

Near-ultraviolet signatures of environment-driven galaxy quenching in Sloan Digital Sky Survey groups

© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. We have investigated the effect of group environment on residual star formation in galaxies, using Galaxy Evolution Explorer near-ultraviolet (NUV) galaxy photometry with the Sloan Digital Sky Survey group catalogue of Yang et al. We compared the (NUV - r) colours of grouped and non-grouped galaxies, and find a significant increase in the fraction of red sequence galaxies with blue (NUV - r) colours outside of groups. When comparing galaxies in mass-matched samples of satellite (non-central), and non-grouped galaxies, we found a > 4σ difference in the distribution of (NUV - r) colours, and an (NUV - r) blue fraction > 3σ higher outside groups. A comparison of satellite and non-grouped samples has found the NUV fraction is a factor of ~2 lower for satellite galaxies between 10 10.5 and 10 10.7 M ⊙ , showing that higher mass galaxies are more likely to have residual star formation when not influenced by a group potential. There was a higher (NUV - r) blue fraction of galaxies with lower Sérsic indices (n < 3) outside of groups, not seen in the satellite sample. We have used stellar population models of Bruzual & Charlot with multiple burst, or exponentially declining star formation histories to find that many of the (NUV - r) blue non-grouped galaxies can be explained by a slow (~2 Gyr) decay of star formation, compared to the satellite galaxies. We suggest that taken together, the difference in (NUV - r) colours between samples can be explained by a population of secularly evolving, non-grouped galaxies, where star formation declines slowly. This slow channel is less prevalent in group environments where more rapid quenching can occur

The Clustering and Halo Masses of Star Forming Galaxies at z<1

We present clustering measurements and halo masses of star forming galaxies at 0.2 < z < 1.0. After excluding AGN, we construct a sample of 22553 24 {\mu}m sources selected from 8.42 deg^2 of the Spitzer MIPS AGN and Galaxy Evolution Survey of Bo\"otes. Mid-infrared imaging allows us to observe galaxies with the highest star formation rates (SFRs), less biased by dust obscuration afflicting the optical bands. We find that the galaxies with the highest SFRs have optical colors which are redder than typical blue cloud galaxies, with many residing within the green valley. At z > 0.4 our sample is dominated by luminous infrared galaxies (LIRGs, L_TIR > 10^11 Lsun) and is comprised entirely of LIRGs and ultra-luminous infrared galaxies (ULIRGs, L_TIR > 10^12 Lsun) at z > 0.6. We observe weak clustering of r_0 = 3-6 Mpc/h for almost all of our star forming samples. We find that the clustering and halo mass depend on L_TIR at all redshifts, where galaxies with higher L_TIR (hence higher SFRs) have stronger clustering. Galaxies with the highest SFRs at each redshift typically reside within dark matter halos of M_halo ~ 10^12.9 Msun/h. This is consistent with a transitional halo mass, above which star formation is largely truncated, although we cannot exclude that ULIRGs reside within higher mass halos. By modeling the clustering evolution of halos, we connect our star forming galaxy samples to their local descendants. Most star forming galaxies at z < 1.0 are the progenitors of L < 2.5L* blue galaxies in the local universe, but star forming galaxies with the highest SFRs (L_TIR >10^11.7 Lsun) at 0.6<z<1.0 are the progenitors of early-type galaxies in denser group environments.Comment: 18 pages, 16 figures, 2 tables. Accepted for publication in the Astrophysical Journa

Galaxy And Mass Assembly (GAMA): understanding the wavelength dependence of galaxy structure with bulge-disc decompositions

With a large sample of bright, low-redshift galaxies with optical–near-IR imaging from the GAMA survey we use bulge-disc decompositions to understand the wavelength-dependent behaviour of single-Sersic structural measurements. We denote the variation in single-Sersic index with wavelength as N, likewise for effective radius we use R. We find that most galaxies with a substantial disc, even those with no discernable bulge, display a high value of N. The increase in Sersic index to longer wavelengths is therefore intrinsic to discs, apparently resulting from radial variations in stellar population and/or dust reddening. Similarly, low values of R (< 1) are found to be ubiquitous, implying an element of universality in galaxy colour gradients. We also study how bulge and disc colour distributions vary with galaxy type. We find that, rather than all bulges being red and all discs being blue in absolute terms, both components become redder for galaxies with redder total colours. We even observe that bulges in bluer galaxies are typically bluer than discs in red galaxies, and that bulges and discs are closer in colour for fainter galaxies. Trends in total colour are therefore not solely due to the colour or flux dominance of the bulge or disc

The X-ray and mid-infrared luminosities in luminous type 1 quasars

Several recent studies have reported different intrinsic correlations between the active galactic nucleus (AGN) mid-IR luminosity (${L}_{\mathrm{MIR}}$) and the rest-frame 2–10 keV luminosity (L X) for luminous quasars. To understand the origin of the difference in the observed {L}_{{\rm{X}}}\mbox{--}{L}_{\mathrm{MIR}} relations, we study a sample of 3247 spectroscopically confirmed type 1 AGNs collected from Boötes, XMM-COSMOS, XMM-XXL-North, and the Sloan Digital Sky Survey quasars in the Swift/XRT footprint spanning over four orders of magnitude in luminosity. We carefully examine how different observational constraints impact the observed {L}_{{\rm{X}}}\mbox{--}{L}_{\mathrm{MIR}} relations, including the inclusion of X-ray-nondetected objects, possible X-ray absorption in type 1 AGNs, X-ray flux limits, and star formation contamination. We find that the primary factor driving the different {L}_{{\rm{X}}}\mbox{--}{L}_{\mathrm{MIR}} relations reported in the literature is the X-ray flux limits for different studies. When taking these effects into account, we find that the X-ray luminosity and mid-IR luminosity (measured at rest-frame $6\,\mu {\rm{m}}$, or ${L}_{6\mu {\rm{m}}}$) of our sample of type 1 AGNs follow a bilinear relation in the log–log plane: $\mathrm{log}{L}_{{\rm{X}}}=(0.84\pm 0.03)\times \mathrm{log}{L}_{6\mu {\rm{m}}}/{10}^{45}$ erg s−1 + (44.60 ± 0.01) for ${L}_{6\mu {\rm{m}}}\lt {10}^{44.79}$ erg s−1, and $\mathrm{log}{L}_{{\rm{X}}}=(0.40\pm 0.03)\times \mathrm{log}{L}_{6\mu {\rm{m}}}/{10}^{45}$ erg s−1 + (44.51 ± 0.01) for ${L}_{6\mu {\rm{m}}}\,\geqslant {10}^{44.79}$ erg s−1. This suggests that the luminous type 1 quasars have a shallower {L}_{{\rm{X}}}\mbox{--}{L}_{6\mu {\rm{m}}} correlation than the approximately linear relations found in local Seyfert galaxies. This result is consistent with previous studies reporting a luminosity-dependent {L}_{{\rm{X}}}\mbox{--}{L}_{\mathrm{MIR}} relation and implies that assuming a linear {L}_{{\rm{X}}}\mbox{--}{L}_{6\mu {\rm{m}}} relation to infer the neutral gas column density for X-ray absorption might overestimate the column densities in luminous quasars

Star-Forming, Rotating Spheroidal Galaxies in the GAMA and SAMI Surveys

The Galaxy And Mass Assembly (GAMA) survey has morphologically identified a class of ‘Little Blue Spheroid’ (LBS) galaxies whose relationship to other classes of galaxies we now examine in detail. Considering a sample of 868 LBSs, we find that such galaxies display similar but not identical colours, specific star formation rates, stellar population ages, mass-to-light ratios, and metallicities to Sd-Irr galaxies. We also find that LBSs typically occupy environments of even lower density than those of Sd-Irr galaxies, where ∼65 per cent of LBS galaxies live in isolation. Using deep, high-resolution imaging from VST KiDS and the new Bayesian, 2D galaxy profile modelling code PROFIT, we further examine the detailed structure of LBSs and find that their Sérsic indices, sizes, and axial ratios are compatible with those of low-mass elliptical galaxies. We then examine SAMI Galaxy survey integral field emission line kinematics for a subset of 62 LBSs and find that the majority (42) of these galaxies display ordered rotation with the remainder displaying disturbed/non-ordered dynamics. Finally, we consider potential evolutionary scenarios for a population with this unusual combination of properties, concluding that LBSs are likely formed by a mixture of merger and accretion processes still recently active in low-redshift dwarf populations. We also infer that if LBS-like galaxies were subjected to quenching in a rich environment, they would plausibly resemble cluster dwarf ellipticals

The causes of the red sequence, the blue cloud, the green valley, and the green mountain

The galaxies found in optical surveys fall in two distinct regions of a diagram of optical colour versus absolute magnitude: the red sequence and the blue cloud, with the green valley in between. We show that the galaxies found in a submillimetre survey have almost the opposite distribution in this diagram, forming a \u27green mountain\u27. We show that these distinctive distributions follow naturally from a single, continuous, curved Galaxy Sequence in a diagram of specific star formation rate versus stellar mass, without there being the need for a separate star-forming galaxy main sequence and region of passive galaxies. The cause of the red sequence and the blue cloud is the geometric mapping between stellar mass/specific star formation rate and absolute magnitude/colour, which distorts a continuous Galaxy Sequence in the diagram of intrinsic properties into a bimodal distribution in the diagram of observed properties. The cause of the green mountain isMalmquist bias in the submillimetre waveband, with submillimetre surveys tending to select galaxies on the curve of the Galaxy Sequence, which have the highest ratios of submillimetre-to-optical luminosity. This effect, working in reverse, causes galaxies on the curve of the Galaxy Sequence to be underrepresented in optical samples, deepening the green valley. The green valley is therefore not evidence (1) for there being two distinct populations of galaxies, (2) for galaxies in this region evolving more quickly than galaxies in the blue cloud and the red sequence, and (3) for rapid-quenching processes in the galaxy population

The Chandra Deep Wide-field Survey: A New Chandra Legacy Survey in the Boötes Field. I. X-Ray Point Source Catalog, Number Counts, and Multiwavelength Counterparts

We present a new, ambitious survey performed with the Chandra X-ray Observatory of the 9.3 deg2 Boötes field of the NOAO Deep Wide-Field Survey. The wide field probes a statistically representative volume of the universe at high redshift. The Chandra Deep Wide-field Survey exploits the excellent sensitivity and angular resolution of Chandra over a wide area, combining 281 observations spanning 15 yr, for a total exposure time of 3.4 Ms, and detects 6891 X-ray point sources down to limiting fluxes of 4.7 × 10−16, 1.5 × 10−16, and 9 ×10−16 erg cm−2 s−1 in the 0.5–7, 0.5–2, and 2–7 keV bands, respectively. The robustness and reliability of the detection strategy are validated through extensive, state-of-the-art simulations of the whole field. Accurate number counts, in good agreement with previous X-ray surveys, are derived thanks to the uniquely large number of point sources detected, which resolve 65.0% ± 12.8% of the cosmic X-ray background between 0.5 and 2 keV and 81.0% ± 11.5% between 2 and 7 keV. Exploiting the wealth of multiwavelength data available on the field, we assign redshifts to ~94% of the X-ray sources, estimate their obscuration, and derive absorption-corrected luminosities. We provide an electronic catalog containing all of the relevant quantities needed for future investigations