ABSTRACT We present a robust measurement and analysis of the rest-frame ultraviolet (UV) luminosity functions at z = 4-8. We use deep Hubble Space Telescope imaging over the Cosmic Assembly ...Near-infrared Deep Extragalactic Legacy Survey/GOODS fields, the Hubble Ultra Deep Field, and the Hubble Frontier Field deep parallel observations near the Abell 2744 and MACS J0416.1-2403 clusters. The combination of these surveys provides an effective volume of 0.6-1.2 × 106 Mpc3 over this epoch, allowing us to perform a robust search for faint 18) and bright (M 21) high-redshift galaxies. We select candidate galaxies using a well-tested photometric redshift technique with careful screening of contaminants, finding a sample of 7446 candidate galaxies at 3.5 8.5, with >1000 galaxies at 6-8. We measure both a stepwise luminosity function for candidate galaxies in our redshift samples, and a Schechter function, using a Markov Chain Monte Carlo analysis to measure robust uncertainties. At the faint end, our UV luminosity functions agree with previous studies, yet we find a higher abundance of UV-bright candidate galaxies at 6. Our best-fit value of the characteristic magnitude is consistent with −21 at 5, which is different than that inferred based on previous trends at lower redshift, and brighter at ∼2 significance than previous measures at z = 6 and 7. At z = 8, a single power law provides an equally good fit to the UV luminosity function, while at z = 6 and 7 an exponential cutoff at the bright end is moderately preferred. We compare our luminosity functions to semi-analytical models, and find that the lack of evolution in is consistent with models where the impact of dust attenuation on the bright end of the luminosity function decreases at higher redshift, although a decreasing impact of feedback may also be possible. We measure the evolution of the cosmic star-formation rate (SFR) density by integrating our observed luminosity functions to , correcting for dust attenuation, and find that the SFR density declines proportionally to (1 ) at 4, which is consistent with observations at 9. Our observed luminosity functions are consistent with a reionization history that starts at 10, completes at 6, and reaches a midpoint (x 0.5) at 6.7 9.4. Finally, using a constant cumulative number density selection and an empirically derived rising star-formation history, our observations predict that the abundance of bright z = 9 galaxies is likely higher than previous constraints, although consistent with recent estimates of bright 10 galaxies.
Fitting synthetic spectral energy distributions (SEDs) to the multiband photometry of galaxies to derive their star formation rates (SFRs), stellar masses, ages, etc. requires making a priori ...assumptions about their star formation histories (SFHs). A widely adopted parametrization of the SFH, the so-called τ models where SFR ∝ e−t/τ is shown to lead to unrealistically low ages when applied to a sample of actively star-forming galaxies at z∼ 2, a problem shared by other SFHs when the age is left as a free parameter in the fitting procedure. This happens because the SED of such galaxies, at all wavelengths, is dominated by their youngest stellar populations, which outshine the older ones. Thus, the SED of such galaxies conveys little information on the beginning of star formation (SF), i.e. on the age of their oldest stellar populations. To cope with this problem, besides τ models (hereafter called direct-τ models), we explore a variety of SFHs, such as constant SFR and inverted-τ models (with SFR ∝ e+t/τ), along with various priors on age, including assuming that SF started at high redshift in all the galaxies in the test sample. We find that inverted-τ models with such latter assumption give SFRs and extinctions in excellent agreement with the values derived using only the UV part of the SED, which is the one most sensitive to ongoing SF and reddening. These models are also shown to accurately recover the SFRs and masses of mock galaxies at z∼ 2 constructed from semi-analytic models, which we use as a further test. All other explored SFH templates do not fulfil these two tests as well as inverted-τ models do. In particular, direct-τ models with unconstrained age in the fitting procedure overestimate SFRs and underestimate stellar mass, and would exacerbate an apparent mismatch between the cosmic evolution of the volume densities of SFR and stellar mass. We conclude that for high-redshift star-forming galaxies an exponentially increasing SFR with a high formation redshift is preferable to other forms of the SFH so far adopted in the literature.
We explore star formation histories (SFHs) of galaxies based on the evolution of the star formation rate stellar mass relation (SFR-M). Using data from the FourStar Galaxy Evolution Survey (ZFOURGE) ...in combination with far-IR imaging from the Spitzer and Herschel observatories we measure the SFR-M relation at 0.5 < z <. Similar to recent works we find that the average infrared spectral energy distributions of galaxies are roughly consistent with a single infrared template across a broad range of redshifts and stellar masses, with evidence for only weak deviations. We find that these two estimates are in broad qualitative agreement, but that there is room for improvement at a more detailed level. At early times the SFHs suggest mass growth rates that are as much as 10 x higher than inferred from the SMF. However, at later times the SFHs under-predict the inferred evolution, as is expected in the case of additional growth due to mergers.
We report the detection of CO(J = 2 → 1) emission from three massive dusty starburst galaxies at z > 5 through molecular line scans in the NSF's Karl G. Jansky Very Large Array (VLA) CO Luminosity ...Density at High Redshift (COLDz) survey. Redshifts for two of the sources, HDF 850.1 (z = 5.183) and AzTEC-3 (z = 5.298), were previously known. We revise a previous redshift estimate for the third source GN10 (z = 5.303), which we have independently confirmed through detections of CO J = 1 → 0, 5 → 4, 6 → 5, and C ii 158 m emission with the VLA and the NOrthern Extended Milllimeter Array. We find that two currently independently confirmed CO sources in COLDz are "optically dark", and that three of them are dust-obscured galaxies at z > 5. Given our survey area of ∼60 arcmin2, our results appear to imply a ∼6-55 times higher space density of such distant dusty systems within the first billion years after the Big Bang than previously thought. At least two of these z > 5 galaxies show star formation rate surface densities consistent with so-called "maximum" starbursts, but we find significant differences in CO excitation between them. This result may suggest that different fractions of the massive gas reservoirs are located in the dense, star-forming nuclear regions-consistent with the more extended sizes of the C ii emission compared to the dust continuum and higher C ii-to-far-infrared luminosity ratios in those galaxies with lower gas excitation. We thus find substantial variations in the conditions for star formation between z > 5 dusty starbursts, which typically have dust temperatures that are ∼57% 25% warmer than starbursts at z = 2-3 due to their enhanced star formation activity.
It has been proposed that the (stellar) mass-(gas) metallicity relation of galaxies exhibits a secondary dependence on star formation rate (SFR), and that the resulting Mlow *-Z-SFR relation may be ...redshift-invariant, i.e., "fundamental." However, conflicting results on the character of the SFR dependence, and whether it exists, have been reported. To gain insight into the origins of the conflicting results, we (1) devise a non-parametric, astrophysically motivated analysis framework based on the offset from the star-forming ("main") sequence at a given Mlow * (relative specific SFR); (2) apply this methodology and perform a comprehensive re-analysis of the local Mlow *-Z-SFR relation, based on SDSS, GALEX, and WISE data; and (3) study the impact of sample selection and of using different metallicity and SFR indicators. We show that metallicity is anti-correlated with specific SFR regardless of the indicators used. We do not find that the relation is spurious due to correlations arising from biased metallicity measurements or fiber aperture effects. We emphasize that the dependence is weak/absent for massive galaxies (log Mlow * > 10.5), and that the overall scatter in the Mlow *-Z-SFR relation does not greatly decrease from the Mlow *-Z relation. We find that the dependence is stronger for the highest SSFR galaxies above the star-forming sequence. This two-mode behavior can be described with a broken linear fit in 12+log(O/H) versus log (SFR/Mlow *), at a given Mlow *. Previous parameterizations used for comparative analysis with higher redshift samples that do not account for the more detailed behavior of the local Mlow *-Z-SFR relation may incorrectly lead to the conclusion that those samples follow a different relationship.
Star formation depends critically on cooling mechanisms in the interstellar medium (ISM); however, thermal properties of gas in galaxies at the peak epoch of star formation (z ∼ 2) remain poorly ...understood. A limiting factor in understanding the multiphase ISM is the lack of multiple tracers detected in the same galaxies, such as Polycyclic Aromatic Hydrocarbon (PAH) emission, a tracer of a critical photoelectric heating mechanism in interstellar gas, and C ii 158 m fine-structure emission, a principal coolant. We present ALMA Band 9 observations targeting C ii in six z ∼ 2 star-forming galaxies with strong Spitzer IRS detections of PAH emission. All six galaxies are detected in dust continuum and marginally resolved. We compare the properties of PAH and C ii emission, and constrain their relationship as a function of total infrared luminosity (LIR) and IR surface density. C ii emission is detected in one galaxy at high signal-to-noise (34 ), and we place a secure upper limit on a second source. The rest of our sample are not detected in C ii likely due to redshift uncertainties and narrow ALMA bandpass windows. Our results are consistent with the deficit in C ii/LIR and PAH/LIR observed in the literature. However, the ratio of C ii to PAH emission at z ∼ 2 is possibly much lower than what is observed in nearby dusty star-forming galaxies. This could be the result of enhanced cooling via O i at high-z, hotter gas and dust temperatures, and/or a reduction in the photoelectric efficiency, in which the coupling between interstellar radiation and gas heating is diminished.
Abstract
The Galaxy Evolution Explorer (GALEX) satellite performed the first and only large-area UV survey, which in tandem with the Sloan Digital Sky Survey (SDSS) has facilitated modeling of the ...spectral energy distributions of low-redshift galaxies and the determination of various galaxy properties, in particular the star formation rate. However, the relatively crude angular resolution of GALEX (5″) made its images susceptible to blending of sources, resulting in potentially biased far-UV and near-UV (NUV) pipeline photometry. To remedy this issue and take advantage of model-fit photometry, we use the EMphot software to obtain forced GALEX photometry for ∼700,000 SDSS galaxies at
z
< 0.3. Positional priors of target galaxies and potentially contaminating neighbors were taken from SDSS. New photometry is based on the best-fitting of three model profiles: optical-like, exponential, and flat. New photometry mitigates blending present in the original pipeline catalogs, which affected 16% of galaxies at a level of >0.2 mag and 2% at a level of >1 mag. Pipeline NUV magnitudes are severely affected (≳1 mag) when the neighbor is brighter than the target galaxy and within 10″, or when the neighbor is fainter and within ∼3″ of the target. New photometry fixes edge-of-detector bias, which affected pipeline photometry by up to 0.1 mag in NUV. We present catalogs with new photometry for GALEX observations of different depths, corresponding to the all-sky imaging survey (AIS), medium imaging survey, and deep imaging survey. Catalogs feature combined magnitudes for multiple detections of the same galaxy in a survey.
Abstract
In the next decade, deep galaxy surveys from telescopes such as the James Webb Space Telescope and Roman Space Telescope will provide transformational data sets that will greatly enhance the ...understanding of galaxy formation during the epoch of reionization (EoR). In this work, we present the Deep Realistic Extragalactic Model (DREaM) for creating synthetic galaxy catalogs. Our model combines dark matter simulations, subhalo abundance matching and empirical models, and includes galaxy positions, morphologies, and spectral energy distributions. The resulting synthetic catalog extends to redshifts
z
∼ 12, and galaxy masses
log
10
(
M
/
M
⊙
)
=
5
covering an area of 1 deg
2
on the sky. We use DREaM to explore the science returns of a 1 deg
2
Roman ultra-deep field (UDF), and to provide a resource for optimizing ultra-deep survey designs. We find that a Roman UDF to ∼30
m
AB
will potentially detect more than 10
6
M
UV
< − 17 galaxies, with more than 10
4
at redshifts
z
> 7, offering an unparalleled data set for constraining galaxy properties during the EoR. Our synthetic catalogs and simulated images are made publicly available to provide the community with a tool to prepare for upcoming data.
We investigate how star-forming galaxies typically assemble their masses at high redshift. Taking advantage of the deep multi-wavelength coverage of the GOODS data set, we select two of the largest ...samples of high-redshift star-forming galaxies based on their UV colors and measure stellar mass of individual galaxies. We use template-fitting photometry to obtain optimal estimates of the fluxes in lower-resolution ground-based and Spitzer images using prior information about galaxy positions, shapes, and orientations. By combining the data and realistic simulations to understand measurement errors and biases, we make a statistically robust determination of stellar mass function (SMF) of the UV-selected star-forming galaxies at z ~ 4 and 5. We report a broad correlation between stellar mass and UV luminosity, such that more UV-luminous galaxies are, on average, also more massive. However, we show that the correlation has a substantial intrinsic scatter, particularly for UV-faint galaxies, evidenced by the fact there is a non-negligible number of UV faint but massive galaxies. Furthermore, we find that the low-mass end of the SMF does not rise as steeply as the UV luminosity function ( alpha sub(UVLF) approx = - (1.7-1.8) while alpha sub(SMF) approx = - (1.3-1.4)) of the same galaxies. In a smooth and continuous formation scenario where star formation rates (SFRs) are sustained at the observed rates for a long time, these galaxies would have accumulated more stellar mass (by a factor of approx =3) than observed and therefore the SMF would mirror more closely that of the UV luminosity function. The relatively shallow slope of the SMF is due to the fact that many of the UV-selected galaxies are not massive enough, and therefore are too faint in their rest-frame optical bands, to be detected in the current observations. Our results favor a more episodic formation history in which SFRs of low-mass galaxies vary significantly over cosmic time, a scenario currently favored by galaxy clustering. Our findings for the UV-faint galaxies at high redshift are in contrast with previous studies on more UV-luminous galaxies, which exhibit a tighter SFR-M sub(star) correlation. The discrepancy may suggest that galaxies at different luminosities may have different evolutionary paths. Such a scenario presents a nontrivial test to theoretical models of galaxy formation.
We measure the sizes of 82 massive galaxies at image utilizing deep HST NICMOS data taken in the GOODS North and South fields. Our sample is almost an order of magnitude larger than previous studies ...at these redshifts, providing the first statistical study of massive galaxy sizes at image, confirming the extreme compactness of these systems. We split our sample into disk-like and spheroid-like galaxies based on their Sersic indices, and find that at a given stellar mass disk-like galaxies at image are a factor of 2.6 +/- 0.3 smaller than present-day equal-mass systems, and spheroid-like galaxies at the same redshifts are 4.3 +/- 0.7 smaller than comparatively massive elliptical galaxies today. At image our results are compatible with both a leveling off, or a mild evolution in size. Furthermore, the high density (image2 x 10 super(10 ) Mimage kpcimage) of massive galaxies at these redshifts, which are similar to present-day globular clusters, possibly makes any further evolution in sizes beyond image unlikely.
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