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Register a new userDifferences and similarities of stellar populations in LAEs and LBGs at $zsim$ 3.4 - 6.8
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The differences between the inherent stellar populations (SPs) of LAEs and LBGs are a key factor in understanding early galaxy formation and evolution. We have run a set of SP burst-like models for a sample of 1,558 sources at $3.4<z<6.8$ from the Survey for High-$z$ Absorption Red and Dead Sources (SHARDS) over the GOODS-N field. This work focuses on the differences between the three different observational subfamilies of our sample: LAE-LBGs, no-Ly$alpha$ LBGs and pure LAEs. Single and double SP synthetic spectra were used to model the SEDs, adopting a Bayesian information criterion to analyse under which situations a second SP is required. We find that the sources are well modelled using a single SP in $sim79%$ of the cases. The best models suggest that pure LAEs are typically young low mass galaxies ($tsim26^{+41}_{-25}$ Myr; $M_{mathrm{star}}sim5.6^{+12.0}_{-5.5}times10^{8} M_{odot}$), undergoing one of their first bursts of star formation. On the other hand, no-Ly$alpha$ LBGs require older SPs ($tsim71pm12$ Myr), and they are substantially more massive ($M_{mathrm{star}}sim3.5pm1.1times10^{9} M_{odot}$). LAE-LBGs appear as the subgroup that more frequently needs the addition of a second SP, representing an old and massive galaxy caught in a strong recent star-forming episode. The relative number of sources found from each subfamily at each $z$ supports an evolutionary scenario from pure LAEs and single SP LAE-LBGs to more massive LBGs. Stellar Mass Functions are also derived, finding an increase of $M^{*}$ with cosmic time and a possible steepening of the low mass slope from $zsim6$ to $zsim5$ with no significant change to $zsim4$. Additionally, we have derived the SFR-$M_{mathrm{star}}$ relation, finding a $mathrm{SFR}propto M_{mathrm{star}}^{beta}$ behaviour with negligible evolution from $zsim4$ to $zsim6$.
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We have undertaken a comprehensive search for both Lyman Alpha Emitters (LAEs) and Lyman Break Galaxies (LBGs) in the SHARDS Survey of the GOODS-N field. SHARDS is a deep imaging survey, made with the 10.4 m Gran Telescopio Canarias (GTC), employing 25 medium band filters in the range from 500 to 941 nm. This is the first time that both LAEs and LBGs are surveyed simultaneously in a systematic way in a large field. We draw a sample of 1558 sources; 528 of them are LAEs. Most of the sources (1434) show rest-frame UV continua. A minority of them (124) are pure LAEs with virtually no continuum detected in SHARDS. We study these sources from $zsim3.35$ up to $zsim6.8$, well into the epoch of reionization. Note that surveys done with just one or two narrow band filters lack the possibility to spot the rest-frame UV continuum present in most of our LAEs. We derive redshifts, Star Formation Rates (SFRs), Ly$alpha$ Equivalent Widths (EWs) and Luminosity Functions (LFs). Grouping within our sample is also studied, finding 92 pairs or small groups of galaxies at the same redshift separated by less than 60 comoving kpc. In addition, we relate 87 and 55 UV-selected objects with two known overdensities at $z=4.05$ and $z=5.198$, respectively. Finally, we show that surveys made with broad band filters are prone to introduce many unwanted sources ($sim20$% interlopers), which means that previous studies may be overestimating the calculated LFs, specially at the faint end.
Giant star-forming regions (clumps) are widespread features of galaxies at $z approx 1-4$. Theory predicts that they can play a crucial role in galaxy evolution if they survive to stellar feedback for > 50 Myr. Numerical simulations show that clumps survival depends on the stellar feedback recipes that are adopted. Up to date, observational constraints on both clumps outflows strength and gas removal timescale are still uncertain. In this context, we study a line-emitting galaxy at redshift $z simeq 3.4$ lensed by the foreground galaxy cluster Abell 2895. Four compact clumps with sizes $lesssim$ 280 pc and representative of the low-mass end of clumps mass distribution (stellar masses $lesssim 2times10^8 {rm M}_odot$) dominate the galaxy morphology. The clumps are likely forming stars in a starbursting mode and have a young stellar population ($sim$ 10 Myr). The properties of the Lyman-$alpha$ (Ly$alpha$) emission and nebular far-ultraviolet absorption lines indicate the presence of ejected material with global outflowing velocities of $sim$ 200-300 km/s. Assuming that the detected outflows are the consequence of star formation feedback, we infer an average mass loading factor ($eta$) for the clumps of $sim$ 1.8 - 2.4 consistent with results obtained from hydro-dynamical simulations of clumpy galaxies that assume relatively strong stellar feedback. Assuming no gas inflows (semi-closed box model), the estimates of $eta$ suggest that the timescale over which the outflows expel the molecular gas reservoir ($simeq 7times 10^8 text{M}_odot$) of the four detected low-mass clumps is $lesssim$ 50 Myr.
We present average stellar population properties and dark matter halo masses of $z sim 2$ lya emitters (LAEs) from SED fitting and clustering analysis, respectively, using $simeq$ $1250$ objects ($NB387le25.5$) in four separate fields of $simeq 1$ deg$^2$ in total. With an average stellar mass of $10.2, pm, 1.8times 10^8 {mathrm M_odot}$ and star formation rate of $3.4, pm, 0.4 {mathrm M_odot} {rm yr^{-1}}$, the LAEs lie on an extrapolation of the star-formation main sequence (MS) to low stellar mass. Their effective dark matter halo mass is estimated to be $4.0_{-2.9}^{+5.1} times 10^{10} {mathrm M_odot}$ with an effective bias of $1.22^{+0.16}_{-0.18}$ which is lower than that of $z sim 2$ LAEs ($1.8, pm, 0.3$), obtained by a previous study based on a three times smaller survey area, with a probability of $96%$. However, the difference in the bias values can be explained if cosmic variance is taken into account. If such a low halo mass implies a low HI gas mass, this result appears to be consistent with the observations of a high lya escape fraction. With the low halo masses and ongoing star formation, our LAEs have a relatively high stellar-to-halo mass ratio (SHMR) and a high efficiency of converting baryons into stars. The extended Press-Schechter formalism predicts that at $z=0$ our LAEs are typically embedded in halos with masses similar to that of the Large Magellanic Cloud (LMC); they will also have similar SHMRs to the LMC, if their SFRs are largely suppressed after $z sim 2$ as some previous studies have reported for the LMC itself.
We are undertaking a search for high-redshift low luminosity Lyman Alpha sources in the SHARDS survey. Among the pre-selected Lyman Alpha sources 2 candidates were spotted, located 3.19 arcsec apart, and tentatively at the same redshift. Here we report on the spectroscopic confirmation with GTC of the Lyman Alpha emission from this pair of galaxies at a confirmed spectroscopic redshifts of z=5.07. Furthermore, one of the sources is interacting/merging with another close companion that looks distorted. Based on the analysis of the spectroscopy and additional photometric data, we infer that most of the stellar mass of these objects was assembled in a burst of star formation 100 Myr ago. A more recent burst (2 Myr old) is necessary to account for the measured Lyman Alpha flux. We claim that these two galaxies are good examples of Lyman Alpha sources undergoing episodic star formation. Besides, these sources very likely constitute a group of interacting Lyman Alpha emitters (LAEs).
Using data from the WISE mission, we have measured near infra-red (NIR) photometry of a diverse sample of dust-free stellar systems (globular clusters, dwarf and giant early-type galaxies) which have metallicities that span the range -2.2 < [Fe/H] (dex) < 0.3. This dramatically increases the sample size and broadens the metallicity regime over which the 3.4 (W1) and 4.6 micron (W2) photometry of stellar populations have been examined. We find that the W1 - W2 colors of intermediate and old (> 2 Gyr) stellar populations are insensitive to the age of the stellar population, but that the W1 - W2 colors become bluer with increasing metallicity, a trend not well reproduced by most stellar population synthesis (SPS) models. In common with previous studies, we attribute this behavior to the increasing strength of the CO absorption feature located in the 4.6 micron bandpass with metallicity. Having used our sample to validate the efficacy of some of the SPS models, we use these models to derive stellar mass-to-light ratios in the W1 and W2 bands. Utilizing observational data from the SAURON and ATLAS3D surveys, we demonstrate that these bands provide extremely simple, yet robust stellar mass tracers for dust free older stellar populations that are freed from many of the uncertainties common among optical estimators.
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