We use a newly assembled sample of 3545 star-forming galaxies with secure spectroscopic, grism, and photometric redshifts at z = 1.5-2.5 to constrain the relationship between UV slope (β) and dust ...attenuation (LIR/LUV IRX). Our sample significantly extends the range of LUV and β probed in previous UV-selected samples, including those as faint as M1600 = −17.4 ( ) and −2.6 β 0.0. IRX is measured using stacks of deep Herschel data, and the results are compared with predictions of the IRX−β relation for different assumptions of the stellar population model and obscuration curve. We find that z = 1.5-2.5 galaxies have an IRX−β relation that is consistent with the predictions for an SMC curve if we invoke subsolar-metallicity models currently favored for high-redshift galaxies, while the commonly assumed starburst curve overpredicts the IRX at a given β by a factor of 3. IRX is roughly constant with LUV for LUV 3 × 109 L . Thus, the commonly observed trend of fainter galaxies having bluer β may simply reflect bluer intrinsic slopes for such galaxies, rather than lower obscurations. The IRX−β relation for young/low-mass galaxies at z 2 implies a dust curve that is steeper than the SMC. The lower attenuations and higher ionizing photon output for low-metallicity stellar populations point to Lyman continuum production efficiencies, ion, that may be elevated by a factor of 2 relative to the canonical value for L* galaxies, aiding in their ability to keep the universe ionized at z ∼ 2.
We present the first results of an Atacama Large Millimeter Array survey of the lower fine-structure line of atomic carbon C i in far-infrared-selected galaxies on the main sequence at z ∼ 1.2 in the ...COSMOS field. We compare our sample with a comprehensive compilation of data available in the literature for local and high-redshift starbursting systems and quasars. We show that the C i (3P1 → 3P0) luminosity correlates on global scales with the infrared luminosity , similar to low-J CO transitions. We report a systematic variation of / as a function of the galaxy type, with the ratio being larger for main-sequence galaxies than for starbursts and submillimeter galaxies at fixed . The / and / mass ratios are similar for main-sequence galaxies and for local and high-redshift starbursts within a 0.2 dex intrinsic scatter, suggesting that C i is a good tracer of molecular gas mass as CO and dust. We derive a fraction of of the total carbon mass in the atomic neutral phase. Moreover, we estimate the neutral atomic carbon abundance, the fundamental ingredient to calibrate C i as a gas tracer, by comparing and available gas masses from CO lines and dust emission. We find lower C i abundances in main-sequence galaxies than in starbursting systems and submillimeter galaxies as a consequence of the canonical CO and gas-to-dust conversion factors. This argues against the application to different galaxy populations of a universal standard C i abundance derived from highly biased samples.
Abstract
We study the physical properties of the ionized gas in local discs using the sample of 38 nearby ∼108.5–11.2 M⊙ Star-Forming Main-Sequence (SFMS) galaxies observed so far as part of the MUSE ...Atlas of Disks (MAD). Specifically, we use all strong emission lines in the MUSE wavelength range 4650–9300 Å to investigate the resolved ionized gas properties on ∼100 pc scales. This spatial resolution enables us to disentangle H ii regions from the diffuse ionized gas (DIG) in the computation of gas metallicities and star formation rates (SFRs) of star-forming regions. The gas metallicities generally decrease with radius. The metallicity of the H ii regions is on average ∼0.1 dex higher than that of the DIG, but the metallicity radial gradient in both components is similar. The mean metallicities within the inner galaxy cores correlate with the total stellar mass of the galaxies. On our < 100 pc scales, we find two correlations previously reported at kpc scales: a spatially resolved mass–metallicity relation (RMZR) and a spatially resolved SFMS (RSFMS). We find no secondary dependence of the RMZR with the SFR density. We find that both resolved relations have a local origin, as they do not depend on the total stellar mass. The observational results of this paper are consistent with the inside-out scenario for the growth of galactic disks.
While the formation of stellar clumps in distant galaxies is usually attributed to gravitational violent disk instabilities, we show here that major mergers also represent a competitive mechanism to ...form bright clumps. Using ∼0.1″ resolution ACS F814W images in the entire COSMOS field, we measured the fraction of clumpy emission in 109 main sequence (MS) and 79 Herschel-detected starbursts (off-MS) galaxies at 0.5 < z < 0.9, representative of normal versus merger induced star-forming activity, respectively. We additionally identify merger samples from visual inspection and from Gini-M20 morphological parameters. Regardless of the merger criteria adopted, the clumpiness distribution of merging systems is different from that of normal isolated disks at a > 99.5% confidence level. The former reaches higher clumpiness values up to 20% of the total galaxy emission. We confirm the merger induced clumpiness enhancement with novel hydrodynamical simulations of colliding galaxies with gas fractions typical of z ∼ 0.7. Multi-wavelength images of three starbursts in the CANDELS field support the young nature of clumps, which are likely merger products rather than older preexisting structures. Finally, for a subset of 19 starbursts with existing near-infrared rest frame spectroscopy, we find that the clumpiness is mildly anti-correlated with the merger phase, which decreases toward final coalescence. Our result can explain recent ALMA detections of clumps in hyperluminous high-z starbursts, while normal objects are smooth. This work raises a question as to the role of mergers on the origin of clumps in high redshift galaxies in general.
A randomly chosen star in today's universe is most likely to live in a galaxy with stellar mass between the Milky Way and Andromeda. It remains uncertain, however, how the structural evolution of ...these bulge-disk systems proceeded. Most of the unobscured star formation we observe by building Andromeda progenitor s at 0.7 < z < 1.5 occurs in disks, but 90% of their star formation is reprocessed by dust and remains unaccounted for. Here we map rest-500 m dust continuum emission in an Andromeda progenitor at z = 1.25 to probe where it is growing through dust-obscured star formation. Combining resolved dust measurements from the NOthern Extended Millimeter Array interferometer with Hubble Space Telescope H maps and multicolor imaging (including new data from the Hubble Deep UV Legacy Survey, HDUV), we find a bulge growing by dust-obscured star formation: while the unobscured star formation is centrally suppressed, the dust continuum is centrally concentrated, filling the ring-like structure that is evident in the H and UV emission. Reflecting this, the dust emission is more compact than the optical/UV tracers of star formation with re(dust) = 3.4 kpc, re(H )/re(dust) = 1.4, and re(UV)/re(dust) = 1.8. Crucially, however, the bulge and disk of this galaxy are building simultaneously; although the dust emission is more compact than the rest-optical emission (re(optical)/re(dust) = 1.4), it is somewhat less compact than the stellar mass (re(M*)/re(dust) = 0.9). Taking the rest-500 m emission as a tracer, the expected structural evolution can be accounted for by star formation: it will grow in size by Δre/ΔM* ∼ 0.3 and in central surface density by Δ cen/ΔM* ∼ 0.9. Finally, our observations are consistent with a picture in which merging and disk instabilities drive gas to the center of galaxies, boosting global star formation rates above the main sequence and building bulges.
We investigate the origin of the evolution of the population-averaged central stellar mass density ( 1) of quiescent galaxies (QGs) by probing the relation between stellar age and 1 at z ∼ 0. We use ...the Zurich ENvironmental Study (ZENS), which is a survey of galaxy groups with a large fraction of satellite galaxies. QGs shape a narrow locus in the 1-M plane, which we refer to as 1 ridgeline. Colors of (B − I) and (I − J) are used to divide QGs into three age categories: young (<2 Gyr), intermediate (2-4 Gyr), and old (>4 Gyr). At fixed stellar mass, old QGs on the 1 ridgeline have higher 1 than young QGs. This shows that galaxies landing on the 1 ridgeline at later epochs arrive with lower 1, which drives the zeropoint of the ridgeline down with time. We compare the present-day zeropoint of the oldest population at z = 0 with the zeropoint of the quiescent population 4 Gyr back in time, at z = 0.37. These zeropoints are identical, showing that the intrinsic evolution of individual galaxies after they arrive on the 1 ridgeline must be negligible, or must evolve parallel to the ridgeline during this interval. The observed evolution of the global zeropoint of 0.07 dex over the last 4 Gyr is thus largely due to the continuous addition of newly quenched galaxies with lower 1 at later times ("progenitor bias"). While these results refer to the satellite-rich ZENS sample as a whole, our work suggests a similar age- 1 trend for central galaxies.
The Zurich Environmental Study (ZENS) is based on a sample of ~1500 galaxy members of 141 groups in the mass range ~10 super(12.5-14.5) M sub(middot in circle) within the narrow redshift range 0.05 < ...z < 0.0585. ZENS adopts novel approaches, described here, to quantify four different galactic environments, namely: (1) the mass of the host group halo; (2) the projected halo-centric distance; (3) the rank of galaxies as central or satellites within their group halos; and (4) the filamentary large-scale structure density. No self-consistent identification of a central galaxy is found in ~40% of <10 super(13.5) M sub(middot in circle) groups, from which we estimate that ~15% of groups at these masses are dynamically unrelaxed systems. Central galaxies in relaxed and unrelaxed groups generally have similar properties, suggesting that centrals are regulated by their mass and not by their environment. Centrals in relaxed groups have, however, ~30% larger sizes than in unrelaxed groups, possibly due to accretion of small satellites in virialized group halos. At M > 10 super(10) M sub(middot in circle), satellite galaxies in relaxed and unrelaxed groups have similar size, color, and (specific) star formation rate distributions; at lower galaxy masses, satellites are marginally redder in relaxed relative to unrelaxed groups, suggesting quenching of star formation in low-mass satellites by physical processes active in relaxed halos. Overall, relaxed and unrelaxed groups show similar stellar mass populations, likely indicating similar stellar mass conversion efficiencies. In the enclosed ZENS catalog, we publish all environmental diagnostics as well as the galaxy structural and photometric measurements described in companion ZENS papers II and III.
ABSTRACT
SKA-MID surveys will be the first in the radio domain to achieve clearly sub-arcsecond resolution at high sensitivity over large areas, opening new science applications for galaxy evolution. ...To investigate the potential of these surveys, we create simulated SKA-MID images of a ∼0.04 deg2 region of GOODS-North, constructed using multi-band HST imaging of 1723 real galaxies containing significant substructure at 0 < z < 2.5. We create images at the proposed depths of the band 2 wide, deep, and ultradeep reference surveys (RMS = 1.0, 0.2, and 0.05 μJy over 1000, 10–30, and 1 deg2, respectively), using the telescope response of SKA-MID at 0.6 arcsec resolution. We quantify the star formation rate – stellar mass space the surveys will probe, and asses to which stellar masses the surveys will be complete. We measure galaxy flux density, half-light radius (R50), concentration, Gini (distribution of flux), second-order moment of the brightest pixels (M20), and asymmetry before and after simulation with the SKA response, to perform input-output tests as a function of depth, separating the effects of convolution and noise. We find that the recovery of Gini and asymmetry is more dependent on survey depth than for R50, concentration and M20. We also assess the relative ranking of parameters before and after observation with SKA-MID. R50 best retains its ranking, while asymmetries are poorly recovered. We confirm that the wide tier will be suited to the study of highly star-forming galaxies across different environments, whilst the ultradeep tier will enable detailed morphological analysis to lower SFRs.
ABSTRACT We present the results of a pilot XMM-Newton and Chandra program aimed at studying the diffuse intragroup medium (IGM) of optically selected nearby groups from the Zurich ENvironmental Study ...(ZENS) catalog. The groups are in a narrow mass range about , a mass scale at which the interplay between the IGM and the group member galaxies is still largely unprobed. X-ray emission from the IGM is detected in the energy band 0.5-2 keV with flux erg s−1 cm−2, which is one order of magnitude fainter than for typical ROSAT groups (RASS). For many groups, we set upper limits on the X-ray luminosity, indicating that the detections are likely probing the upper envelope of the X-ray emitting groups. We find that weighting the group halo mass by the fraction of the total stellar mass locked in the bulge galaxy components might reduce the bias of mass estimates based on the total optical luminosity with respect to the X-ray mass estimates, (consistent with Andreon, at larger mass scales). We measure a stellar mass fraction with a median value of about 1%, with a contribution from the most massive galaxies between 30% and 50%. Optical and X-ray data often give complementary answers concerning the dynamical state of the groups, and are essential for a complete picture of the group system. Extending this pilot program to a larger sample of groups is necessary to unveil any imprint of interaction between member galaxies and IGM in halo potentials of key importance for environmentally driven galactic evolution.
PDF
