Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPhysical Properties of Spectroscopically-Confirmed Galaxies at $zge6$. III. Stellar Populations from SED Modeling with Secure Ly$alpha$ Emission and Redshifts
99
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present a study of stellar populations in a sample of spectroscopically-confirmed Lyman-break galaxies (LBGs) and Ly$alpha$ emitters (LAEs) at $5.7<z<7$. These galaxies have deep optical and infrared images from Subaru, $HST$, and $Spitzer$/IRAC. We focus on a subset of 27 galaxies with IRAC detections, and characterize their stellar populations utilizing galaxy synthesis models based on the multi-band data and secure redshifts. By incorporating nebular emission estimated from the observed Ly$alpha$ flux, we are able to break the strong degeneracy of model spectra between young galaxies with prominent nebular emission and older galaxies with strong Balmer breaks. The results show that our galaxies cover a wide range of ages from several to a few hundred million years (Myr), and a wide range of stellar masses from $sim10^8$ to $sim10^{11}$ $M_{odot}$. These galaxies can be roughly divided into an `old subsample and a `young subsample. The `old subsample consists of galaxies older than 100 Myr, with stellar masses higher than $10^9$ $M_{odot}$. The galaxies in the `young subsample are younger than $sim$30 Myr, with masses ranging between $sim10^8$ and $sim3times10^9$ $M_{odot}$. Both subsamples display a correlation between stellar mass and star-formation rate (SFR), but with very different normalizations. The average specific SFR (sSFR) of the `old subsample is 3--4 Gyr$^{-1}$, consistent with previous studies of `normal star-forming galaxies at $zge6$. The average sSFR of the `young subsample is an order of magnitude higher, likely due to starburst activity. Our results also indicate little or no dust extinction in the majority of the galaxies, as already suggested by their steep rest-frame UV slopes. Finally, LAEs and LBGs with strong Ly$alpha$ emission are indistinguishable in terms of age, stellar mass, and SFR.
rate research
Read More
The aim of this paper is to investigate spectral and photometric properties of 854 faint ($i_{AB}$<~25 mag) star-forming galaxies (SFGs) at 2<z<2.5 using the VIMOS Ultra-Deep Survey (VUDS) spectroscopic data and deep multi-wavelength photometric data in three extensively studied extragalactic fields (ECDFS, VVDS, COSMOS). These SFGs were targeted for spectroscopy based on their photometric redshifts. The VUDS spectra are used to measure the UV spectral slopes ($beta$) as well as Ly$alpha$ equivalent widths (EW). On average, the spectroscopically measured $beta$ (-1.36$pm$0.02), is comparable to the photometrically measured $beta$ (-1.32$pm$0.02), and has smaller measurement uncertainties. The positive correlation of $beta$ with the Spectral Energy Distribution (SED)-based measurement of dust extinction, E$_{rm s}$(B-V), emphasizes the importance of $beta$ as an alternative dust indicator at high redshifts. To make a proper comparison, we divide these SFGs into three subgroups based on their rest-frame Ly$alpha$ EW: SFGs with no Ly$alpha$ emission (SFG$_{rm N}$; EW$le$0AA), SFGs with Ly$alpha$ emission (SFG$_{rm L}$; EW$>$0AA), and Ly$alpha$ emitters (LAEs; EW$ge$20AA). The fraction of LAEs at these redshifts is $sim$10%, which is consistent with previous observations. We compared best-fit SED-estimated stellar parameters of the SFG$_{rm N}$, SFG$_{rm L}$ and LAE samples. For the luminosities probed here ($sim$L$^*$), we find that galaxies with and without Ly$alpha$ in emission have small but significant differences in their SED-based properties. We find that LAEs have less dust, and lower star-formation rates (SFR) compared to non-LAEs. We also find that LAEs are less massive compared to non-LAEs, though the difference is smaller and less significant compared to the SFR and E$_{rm s}$(B-V). [abridged]
We present rest-frame optical spectra of 60 faint ($R_{AB}sim 27$; $Lsim0.1 L_*$) Ly$alpha$-selected galaxies (LAEs) at $zapprox2.56$. The average LAE is consistent with the extreme low-metallicity end of the continuum-selected galaxy distribution at $zapprox2-3$. In particular, the LAEs have extremely high [OIII] $lambda$5008/H$beta$ ratios (log([OIII]/H$beta$) $sim$ 0.8) and low [NII] $lambda$6585/H$alpha$ ratios (log([NII]/H$alpha$) $<-1.15$). Using the [OIII] $lambda$4364 auroral line, we find that the star-forming regions in faint LAEs are characterized by high electron temperatures ($T_eapprox1.8times10^4$K), low oxygen abundances (12 + log(O/H) $approx$ 8.04, $Z_{neb}approx0.22Z_odot$), and high excitations with respect to more luminous galaxies. Our faintest LAEs have line ratios consistent with even lower metallicities, including six with 12 + log(O/H) $approx$ 6.9$-$7.4 ($Z_{neb}approx0.02-0.05Z_odot$). We interpret these observations in light of new models of stellar evolution (including binary interactions). We find that strong, hard ionizing continua are required to reproduce our observed line ratios, suggesting that faint galaxies are efficient producers of ionizing photons and important analogs of reionization-era galaxies. Furthermore, we investigate physical trends accompanying Ly$alpha$ emission across the largest current sample of combined Ly$alpha$ and rest-optical galaxy spectroscopy, including 60 faint LAEs and 368 more luminous galaxies at similar redshifts. We find that Ly$alpha$ emission is strongly correlated with nebular excitation and ionization and weakly correlated with dust attenuation, suggesting that metallicity plays a strong role in determining the observed properties of these galaxies by modulating their stellar spectra, nebular excitation, and dust content.
The scatter in the relationship between the strength of [CII] 158$mu$m emission and the star formation rate at high-redshift has been the source of much recent interest. Although the relationship is well-established locally, several intensely star-forming galaxies have been found whose [CII] 158$mu$m emission is either weak, absent or spatially offset from the young stars. Here we present new ALMA data for the two most distant, gravitationally-lensed and spectroscopically-confirmed galaxies, A2744_YD4 at $z=$8.38 and MACS1149_JD1 at $z=$9.11, both of which reveal intense [OIII] 88$mu$m emission. In both cases we provide stringent upper limits on the presence of [CII] 158$mu$m with respect to [OIII] 88$mu$m. We review possible explanations for this apparent redshift-dependent [CII] deficit in the context of our recent hydrodynamical simulations. Our results highlight the importance of using several emission line diagnostics with ALMA to investigate the nature of the interstellar medium in early galaxies.
The reionization of the Universe is thought to have been completed by redshifts $zsimeq5.5$. Observations of galaxies in the Subaru Deep Field (SDF) found more than 100 galaxies at $zsimeq6$, many spectroscopically confirmed through follow-up observations. Among a sample of such 67 galaxies, seven galaxies were examined previously, and six showed steep UV-Continuum slopes ($beta$) between $-3.4<beta<-2.6$, indicating young stellar populations. Using the CIGALE package, we model the SEDs of 47 SDF galaxies with Subaru WFCAM K-band data of the seven galaxies studied previously, using a large model parameter space. The seven blue-$beta$ galaxies are compared to the other 40 SDF galaxies to trace any differences or possible relationships in e.g. the model-implied SED age, dust extinction, and the Lyman continuum (LyC) escape fraction $f_{esc}$. We found that the average implied $f_{esc}$ value is $sim42%$, exceeding the minimum for galaxies to finish reionization at $zsimeq6$. Furthermore, we found slight trends between the CIGALE UV-slope, $f_{esc}$, and E(B-V) values: for a given CIGALE E(B-V) value, the implied $beta$ values are steeper than at $z=0$. Lower implied CIGALE $f_{esc}$ values appear to be associated with bluer $beta$ and lower E(B-V), but the trends between the parameters are weak. This suggests that LyC could have escaped through holes in the surrounding the ISM produced by outflows from supernovae and/or weak AGN, with sufficiently wide opening angles for on average $42%$ of the LyC to escape. Further IR spectroscopic observations with the emph{James Webb Space Telescope} will be needed to constrain this possibility.
We study the average Ly$alpha$ emission associated with high-$z$ strong (log $N$(H I) $ge$ 21) damped Ly$alpha$ systems (DLAs). We report Ly$alpha$ luminosities ($L_{rm Lyalpha}$) for the full as well as various sub-samples based on $N$(H I), $z$, $(r-i)$ colours of QSOs and rest equivalent width of Si II$lambda$1526 line (i.e., $W_{1526}$). For the full sample, we find $L_{rm Lyalpha}$$< 10^{41} (3sigma) rm erg s^{-1}$ with a $2.8sigma$ level detection of Ly$alpha$ emission in the red part of the DLA trough. The $L_{rm Lyalpha}$ is found to be higher for systems with higher $W_{1526}$ with its peak, detected at $geq 3sigma$, redshifted by about 300-400 $rm km s^{-1}$ with respect to the systemic absorption redshift, as seen in Lyman Break Galaxies (LBGs) and Ly$alpha$ emitters. A clear signature of a double-hump Ly$alpha$ profile is seen when we consider $W_{1526} ge 0.4$ AA and $(r-i) < 0.05$. Based on the known correlation between metallicity and $W_{1526}$, we interpret our results in terms of star formation rate (SFR) being higher in high metallicity (mass) galaxies with high velocity fields that facilitates easy Ly$alpha$ escape. The measured Ly$alpha$ surface brightness requires local ionizing radiation that is 4 to 10 times stronger than the metagalactic UV background at these redshifts. The relationship between the SFR and surface mass density of atomic gas seen in DLAs is similar to that of local dwarf and metal poor galaxies. We show that the low luminosity galaxies will contribute appreciably to the stacked spectrum if the size-luminosity relation seen for H I at low-$z$ is also present at high-$z$. Alternatively, large Ly$alpha$ halos seen around LBGs could also explain our measurements.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
