Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA Rest-frame Optical View on z~4 Galaxies I: Color and Age Distributions from Deep IRAC Photometry of the IUDF10 and GOODS Surveys
131
0
0.0
(
0
)
Authors
P. A. Oesch
Ask ChatGPT about the research
No Arabic abstract
We present a study of rest-frame UV-to-optical color distributions for z~4 galaxies based on the combination of deep HST/ACS+WFC3/IR data with Spitzer/IRAC imaging. In particular, we use new, ultra-deep data from the IRAC Ultradeep Field program (IUDF10). Our sample contains a total of ~2600 galaxies selected as B-dropout Lyman Break Galaxies (LBGs) in the HUDF and one of its deep parallel fields, the HUDF09-2, as well as GOODS-North and South. This sample is used to investigate the UV continuum slopes beta and Balmer break colors (J_125-[4.5]) as a function of rest-frame optical luminosity. The [4.5] filter is chosen to avoid potential contamination by strong rest-frame optical emission lines. We find that galaxies at M_z<-21.5 (roughly corresponding to L*[z~4]) are significantly redder than their lower luminosity counterparts. The UV continuum slopes and the J_125-[4.5] colors are well correlated. The most simple explanation for this correlation is that the dust reddening at these redshifts is better described by an SMC-like extinction curve, rather than the typically assumed Calzetti reddening. After correcting for dust, we find that the galaxy population shows mean stellar population ages in the range 10^8.5 to 10^9 yr, with a dispersion of ~0.5 dex, and only weak trends as a function of luminosity. In contrast to some results from the literature, we find that only a small fraction of galaxies shows Balmer break colors which are consistent with extremely young ages, younger than 100 Myr. Under the assumption of smooth star-formation histories, this fraction is only 12-19% for galaxies at M_z<-19.75. Our results are consistent with a gradual build-up of stars and dust in galaxies at z>4, with only a small fraction of stars being formed in short, intense bursts of star-formation.
rate research
Read More
We use the high angular resolution in the near-infrared of the WFC3 on HST to determine YHVz color-color selection criteria to identify and characterize 1.5<z<3.5 galaxies in the HUDF09 and ERS (GOODS-South) fields. The WFC3 NIR images reveal galaxies at these redshifts that were undetected in the rest-frame UV HUDF/GOODS images, as well as true centers and regular disks in galaxies classified as highly irregular in rest-frame UV light. Across the 1.5<z<2.15 redshift range, regular disks are unveiled in the WFC3 images of ~25% of both intermediate and high mass galaxies, i.e., above 10^10 Msun. Meanwhile, galaxies maintaining diffuse and/or irregular morphologies in the rest-frame optical light---i.e., not yet dynamically settled---at these epochs are almost entirely restricted to masses below 10^11 Msun. In contrast at 2.25 < z < 3.5 these diffuse and/or irregular structures overwhelmingly dominate the morphological mix in both the intermediate and high mass regimes, while no regular disks, and only a small fraction (25%) of smooth spheroids, are evident above 10^11 Msun. Strikingly, by 1.5 < z < 2.25 roughly 2 out of every 3 galaxies at the highest masses are spheroids. In our small sample, the fraction of star-forming galaxies at these mass scales decreases concurrently from ~60% to ~5%. If confirmed, this indicates that z~2 is the epoch of both the morphological transformation and quenching of star-formation which assemble the first substantial population of massive ellipticals.
We present Keck II NIRSPEC rest-frame optical spectra for three recently discovered lensed galaxies: the Cosmic Horseshoe (z = 2.38), the Clone (z = 2.00), and SDSS J090122.37+181432.3 (z = 2.26). The boost in signal-to-noise ratio (S/N) from gravitational lensing provides an unusually detailed view of the physical conditions in these objects. A full complement of high S/N rest-frame optical emission lines is measured, spanning from rest-frame 3600 to 6800AA, including robust detections of fainter lines such as H-gamma, [SII]6717,6732, and in one instance [NeII]3869. SDSS J090122.37+181432.3 shows evidence for AGN activity, and therefore we focus our analysis on star-forming regions in the Cosmic Horseshoe and the Clone. For these two objects, we estimate a wide range of physical properties, including star-formation rate (SFR), metallicity, dynamical mass, and dust extinction. In all respects, the lensed objects appear fairly typical of UV-selected star-forming galaxies at z~2. The Clone occupies a position on the emission-line diagnostic diagram of [OIII]/H-beta vs. [NII]/H-alpha that is offset from the locations of z~0 galaxies. Our new NIRSPEC measurements may provide quantitative insights into why high-redshift objects display such properties. From the [SII] line ratio, high electron densities (~1000 cm^(-3)) are inferred compared to local galaxies, and [OIII]/[OII] line ratios indicate higher ionization parameters compared to the local population. Building on previous similar results at z~2, these measurements provide further evidence (at high S/N) that star-forming regions are significantly different in high-redshift galaxies, compared to their local counterparts (abridged).
Euclid, WFIRST, and HETDEX will make emission-line selected galaxies the largest observed constituent in the $z > 1$ universe. However, we only have a limited understanding of the physical properties of galaxies selected via their Ly$alpha$ or rest-frame optical emission lines. To begin addressing this problem, we present the basic properties of $sim 2,000$ AEGIS, COSMOS, GOODS-N, GOODS-S, and UDS galaxies identified in the redshift range $1.90 < z < 2.35$ via their [O II], H$beta$, and [O III] emission lines. For these $z sim 2$ galaxies, [O III] is generally much brighter than [O II] and H$beta$, with typical rest-frame equivalent widths of several hundred Angstroms. Moreover, these strong emission-line systems span an extremely wide range of stellar mass ($sim 3$ dex), star-formation rate ($sim 2$ dex), and [O III] luminosity ($sim 2$ dex). Comparing the distributions of these properties to those of continuum selected galaxies, we find that emission-line galaxies have systematically lower stellar masses and lower optical/UV dust attenuations. These measurements lay the groundwork for an extensive comparison between these rest-frame optical emission-line galaxies and Ly$alpha$ emitters identified in the HETDEX survey.
We study the evolution of galaxy rest-frame ultraviolet (UV) colors in the epoch 4 < z < 8. We use new wide-field near-infrared data in GOODS-S from the CANDELS, HUDF09 and ERS programs to select galaxies via photometric redshift measurements. Our sample consists of 2812 candidate galaxies at z > 3.5, including 113 at z = 7 to 8. We fit the observed spectral energy distribution to a suite of synthetic stellar population models, and measure the value of the UV spectral slope (beta) from the best-fit model spectrum. The median value of beta evolves significantly from -1.82 (+0.00,-0.04) at z = 4, to -2.37 (+0.26,-0.06) at z = 7. Additionally, we find that faint galaxies at z = 7 have beta = -2.68 (+0.39,-0.24) (~ -2.4 after correcting for observational bias); this is redder than previous claims in the literature, and does not require exotic stellar populations to explain their colors. This evolution can be explained by an increase in dust extinction, with the timescale consistent with low-mass AGB stars forming the bulk of the dust. We find no significant (< 2-sigma) correlation between beta and M_UV when measuring M_UV at a consistent rest-frame wavelength of 1500 A. This is particularly true at bright magnitudes, though our results do show evidence for a weak correlation at faint magnitudes when galaxies in the HUDF are considered separately, hinting that dynamic range in sample luminosities may play a role. We do find a strong correlation between beta and the stellar mass at all redshifts, in that more massive galaxies exhibit redder colors. The most massive galaxies in our sample have red colors at each redshift, implying that dust can build up quickly in massive galaxies, and that feedback is likely removing dust from low-mass galaxies at z > 7. Thus the stellar-mass - metallicity relation, previously observed up to z ~ 3, may extend out to z = 7 - 8.
We apply a new approach to quantifying galaxy morphology and identifying galaxy mergers to the rest-frame far-ultraviolet images of 82 z ~ 4 Lyman break galaxies (LBGs) and 55 1.2 < z < 1.8 emission-line galaxies in the GOODS and Ultra Deep Fields. We compare the distributions of the Gini coefficient (G), second-order moment of the brightest 20% of galaxy light (M20), and concentration (C) for high-redshift and low-redshift galaxies with average signal to noise per pixel > 2.5 and Petrosian radii > 0.3 arcsec. Ten of the 82 LBGs have M20 >= -1.1 and possess bright double or multiple nuclei, implying a major-merger fraction of star-forming galaxies ~ 10-25% at M_{FUV} < -20, depending on our incompleteness corrections. Galaxies with bulge-like morphologies (G >= 0.55, M20 < -1.6) make up ~ 30% of the z ~ 4 LBG sample, while the remaining ~ 50% have G and M20 values higher than expected for smooth bulges and disks and may be star-forming disks, minor-mergers or post-mergers. The star-forming z ~ 1.5 galaxy sample has a morphological distribution which is similar to the UDF z ~ 4 LBGs, with an identical fraction of major-merger candidates but fewer spheroids. The observed morphological distributions are roughly consistent with current hierarchical model predictions for the major-merger rates and minor-merger induced starbursts at z ~ 1.5 and ~4. We also examine the rest-frame FUV-NUV and FUV-B colors as a function of morphology and find no strong correlations at either epoch.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
