We present the average metallicity and star formation rate (SFR) of Ly alpha emitters (LAEs) measured from our large-area survey with three narrowband (NB) filters covering the Ly alpha , ...OIIlambda3727, and H alpha +Nii lines of LAEs at z = 2.2. We select 919 z = 2.2 LAEs from Subaru/Suprime-Cam NB data in conjunction with Magellan/IMACS spectroscopy. Of these LAEs, 561 and 105 are observed with KPNO/NEWFIRM near-infrared NB filters whose central wavelengths are matched to red-shifted Oii and H alpha nebular lines, respectively. The stacked object has an H alpha luminosity of 1.7 x 1042 erg ssup -1 corresponding to an SFR of 14M yrsup -1. We place, for the first time, a firm lower limit to the average metallicity of LAEs of Z> or =0.09Z (2 delta ) based on the OII/(H alpha +Nii) index together with photoionization models and empirical relations. The H alpha and Ly alpha luminosities of our NB-selected LAEs indicate that the escape fraction of Ly alpha photons is ~12%-30%, much higher than the values derived for other galaxy populations at z~2.
Abstract
We investigate the relationship between dust attenuation and stellar mass (
M
*
) in star-forming galaxies over cosmic time. For this analysis, we compare measurements from the MOSFIRE Deep ...Evolution Field survey at
z
∼ 2.3 and the Sloan Digital Sky Survey (SDSS) at
z
∼ 0, augmenting the latter optical data set with both UV Galaxy Evolution Explorer (GALEX) and mid-infrared Wide-field Infrared Survey Explorer (WISE) photometry from the GALEX-SDSS-WISE Catalog. We quantify dust attenuation using both spectroscopic measurements of H
α
and H
β
emission lines, and photometric measurements of the rest-UV stellar continuum. The H
α
/H
β
ratio is used to determine the magnitude of attenuation at the wavelength of H
α
,
A
H
α
. Rest-UV colors and spectral energy distribution fitting are used to estimate
A
1600
, the magnitude of attenuation at a rest wavelength of 1600 Å. As in previous work, we find a lack of significant evolution in the relation between dust attenuation and
M
*
over the redshift range
z
∼ 0 to
z
∼ 2.3. Folding in the latest estimates of the evolution of
M
dust
, (
M
dust
/
M
gas
), and gas surface density at fixed
M
*
, we find that the expected
M
dust
and dust mass surface density are both significantly higher at
z
∼ 2.3 than at
z
∼ 0. These differences appear at odds with the lack of evolution in dust attenuation. To explain the striking constancy in attenuation versus
M
*
, it is essential to determine the relationship between metallicity and (
M
dust
/
M
gas
), the dust mass absorption coefficient and dust geometry, and the evolution of these relations and quantities from
z
∼ 0 to
z
∼ 2.3.
We study the dependence of star formation quenching on galaxy mass and environment, in the Sloan Digital Sky Survey (SDSS; z ∼ 0.1) and the All-Wavelength Extended Groth Strip International Survey ...(AEGIS; z ∼ 1). It is crucial that we define quenching by low star formation rate rather than by red colour, given that one-third of the red galaxies are star forming. We address stellar mass M
*, halo mass M
h, density over the nearest N neighbours δ
N
and distance to the halo centre D. The fraction of quenched galaxies appears more strongly correlated with M
h at fixed M
* than with M
* at fixed M
h, while for satellites quenching also depends on D. We present the M
*-M
h relation for centrals at z ∼ 1. At z ∼ 1, the dependence of quenching on M
* at fixed M
h is somewhat more pronounced than at z ∼ 0, but the quenched fraction is low (10 per cent) and the haloes are less massive. For satellites, M
*-dependent quenching is noticeable at high D, suggesting a quenching dependence on subhalo mass for recently captured satellites. At small D, where satellites likely fell in more than a few Gyr ago, quenching strongly depends on M
h and not on M
*. The M
h dependence of quenching is consistent with theoretical wisdom where virial shock heating in massive haloes shuts down accretion and triggers ram-pressure stripping, causing quenching. The interpretation of δ
N
is complicated by the fact that it depends on the number of observed group members compared to N, motivating the use of D as a better measure of local environment.
This paper examines star formation (SF) in relatively massive, primarily early-type galaxies (ETGs) at z ~ 0.1. A sample is drawn from bulge-dominated Galaxy Evolution Explorer/Sloan Digital Sky ...Survey (GALEX/SDSS) galaxies on the optical red sequence with strong UV excess and yet quiescent SDSS spectra. High-resolution far-UV imaging of 27 such ETGs using Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel (ACS/SBC) reveals structured UV morphology in 93% of the sample, consistent with low-level ongoing SF (~0.5 M sub(middot in circle) yr super(-1)). In 3/4 of the sample the SF is extended on galaxy scales (25-75 kpc), while the rest contains smaller (5-15 kpc) SF patches in the vicinity of an ETG-presumably gas-rich satellites being disrupted. Optical imaging reveals that all ETGs with galaxy-scale SF in our sample have old stellar disks (mostly S0 type). None is classified as a true elliptical. In our sample, galaxy-scale SF takes the form of UV rings of varying sizes and morphologies. For the majority of such objects we conclude that the gas needed to fuel current SF has been accreted from the intergalactic medium, probably in a prolonged, quasi-static manner, leading in some cases to additional disk buildup. The remaining ETGs with galaxy-scale SF have UV and optical morphologies consistent with minor merger-driven SF or with the final stages of SF in fading spirals. Our analysis excludes that all recent SF on the red sequence resulted from gas-rich mergers. We find further evidence that galaxy-scale SF is almost exclusively an S0 phenomenon (~20% S0s have SF) by examining the overall optically red SDSS ETGs. Conclusion is that significant number of field S0s maintain or resume low-level SF because the preventive feedback is not in place or is intermittent. True ellipticals, on the other hand, stay entirely quiescent even in the field.
The shutdown of star formation in galaxies is generally termed "quenching." This paper addresses quenching by searching for traces of possible quenching processes through their effects on galaxy ...structural parameters such as stellar mass (M sub(*)), M sub(*)/r sub(e), surface stellar mass density (~M sub(*)/r super(2) sub(e)), and Sersic index (n). We analyze the rest-frame U-B color correlations versus these structural parameters using a sample of galaxies in the redshift range 0.5 < or =, slant z < 0.8 from the DEEP2/AEGIS survey. We assess the tightness of the color relationships by measuring their "overlap regions," defined as the area in color-parameter space in which red and blue galaxies overlap; the parameter that minimizes these overlap regions is considered to be the most effective color discriminator. We discuss a two-stage model for quenching in which galaxy star formation rates are controlled by their dark halos while they are still in the blue cloud and a second quenching process sets in later, associated with the central stellar mass buildup.
ABSTRACT
The colour bimodality of galaxies provides an empirical basis for theories of galaxy evolution. However, the balance of processes that begets this bimodality has not yet been constrained. A ...more detailed view of the galaxy population is needed, which we achieve in this paper by using unsupervised machine learning to combine multidimensional data at two different epochs. We aim to understand the cosmic evolution of galaxy subpopulations by uncovering substructures within the colour bimodality. We choose a clustering algorithm that models clusters using only the most discriminative data available, and apply it to two galaxy samples: one from the second edition of the GALEX-SDSS-WISE Legacy Catalogue (GSWLC-2; z ∼ 0.06), and the other from the VIMOS Public Extragalactic Redshift Survey (VIPERS; z ∼ 0.65). We cluster within a nine-dimensional feature space defined purely by rest-frame ultraviolet-through-near-infrared colours. Both samples are similarly partitioned into seven clusters, breaking down into four of mostly star-forming galaxies (including the vast majority of green valley galaxies) and three of mostly passive galaxies. The separation between these two families of clusters suggests differences in the evolution of their galaxies, and that these differences are strongly expressed in their colours alone. The samples are closely related, with star-forming/green-valley clusters at both epochs forming morphological sequences, capturing the gradual internally driven growth of galaxy bulges. At high stellar masses, this growth is linked with quenching. However, it is only in our low-redshift sample that additional, environmental processes appear to be involved in the evolution of low-mass passive galaxies.
ABSTRACT Improving our knowledge of global Milky Way (MW) properties is critical for connecting the detailed measurements only possible from within our Galaxy to our understanding of the broader ...galaxy population. We here train Gaussian process regression (GPR) models on SDSS (Sloan Digital Sky Survey) galaxies to map from galaxy properties (stellar mass, apparent axial ratio, star formation rate, bulge-to-total ratio, disc scale length, and bar vote fraction) to ultraviolet (UV; GALEX FUV/NUV), optical (SDSS ugriz), and infrared (IR; 2MASS JHKs and WISE W1/W2/W3/W4) fluxes and uncertainties. With these models, we estimate the photometric properties of the MW, resulting in a full UV-to-IR spectral energy distribution (SED) as it would be measured externally, viewed face-on. We confirm that the MW lies in the green valley in optical diagnostic diagrams, but show for the first time that the MW is in the star-forming region in standard UV and IR diagnostics – characteristic of the population of red spiral galaxies. Although our GPR method predicts one band at a time, the resulting MW UV–IR SED is consistent with SEDs of local spirals with characteristics broadly similar to the MW, suggesting that these independent predictions can be combined reliably. Our UV–IR SED will be invaluable for reconstructing the MW’s star formation history using the same tools employed for external galaxies, allowing comparisons of results from in situ measurements to those from the methods used for extragalactic objects.
We present measurements of the dust attenuation of H alpha -selected emission-line galaxies at z = 0.8 from the NewH alpha narrowband survey. The analysis is based on deep follow-up spectroscopy with ...Magellan/IMACS, which captures the strong rest-frame optical emission lines from OII lambda3727 to OIII lambda5007. We place constraints on the active galactic nucleus (AGN) fraction using diagnostics that can be applied at intermediate redshift. We measure the dust attenuation for individual objects from the ratios of the higher order Balmer lines. We also create stacked spectra to probe the attenuation in objects without individual detections. Both the results from the individual z = 0.8 galaxies and from the stacked spectra show consistency with the mass-attenuation and SFR-attenuation relations found in the local universe, indicating that these relations are also applicable at intermediate redshift.
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