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Register a new userOn the UV compactness and morphologies of typical Lyman-a emitters from z~2 to z~6
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We investigate the rest-frame UV morphologies of a large sample of Lyman-a emitters (LAEs) from z~2 to z~6, selected in a uniform way with 16 different narrow- and medium-bands over the full COSMOS field. We use 3045 LAEs with HST coverage in a stacking analysis and find that they have M_UV~-20, below M*_UV at these redshifts. We also focus our analysis on a subsample of 780 individual galaxies with i_AB<25 for which GALFIT converges for 429 of them. The individual median size (re~1 kpc), ellipticities (slightly elongated with (b/a)~0.45), Sersic index (disk-like with n<2) and light concentration (comparable to that of disk or irregular galaxies, with C~2.7) of LAEs show mild evolution from z~2 to z~6. LAEs with the highest rest-frame equivalent widths (EW) are the smallest/most compact (re~0.8 kpc, compared to re~1.5 kpc for the lower EW LAEs). When stacking our samples in bins of fixed Lya luminosity and Lya EW we find evidence for redshift evolution in n and C, but not in galaxy sizes. The evolution seems to be stronger for LAEs with 25<EW<100 {AA}. When compared to other SFGs, LAEs are found to be smaller at all redshifts. The difference between the two populations changes with redshift, from a factor of ~1 at z>5 to SFGs being a factor of ~2-4 larger than LAEs for z<2. This means that at the highest redshifts, where typical sizes approach those of LAEs, the fraction of galaxies showing Lya in emission (and with a high Lya escape fraction) should be much higher, consistent with observations.
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We measure the evolution of the rest-frame UV luminosity function (LF) and the stellar mass function (SMF) of Lyman-alpha (Lya) emitters (LAEs) from z~2 to z~6 by exploring ~4000 LAEs from the SC4K sample. We find a correlation between Lya luminosity (LLya) and rest-frame UV (M_UV), with best-fit M_UV=-1.6+-0.2 log10(LLya/erg/s)+47+-12 and a shallower relation between LLya and stellar mass (Mstar), with best-fit log10( Mstar/Msun)=0.9+-0.1 log10(LLya/erg/s)-28+-4.0. An increasing LLya cut predominantly lowers the number density of faint M_UV and low Mstar LAEs. We estimate a proxy for the full UV LFs and SMFs of LAEs with simple assumptions of the faint end slope. For the UV LF, we find a brightening of the characteristic UV luminosity (M_UV*) with increasing redshift and a decrease of the characteristic number density (Phi*). For the SMF, we measure a characteristic stellar mass (Mstar*/Msun) increase with increasing redshift, and a Phi* decline. However, if we apply a uniform luminosity cut of log10 (LLya/erg/s) >= 43.0, we find much milder to no evolution in the UV and SMF of LAEs. The UV luminosity density (rho_UV) of the full sample of LAEs shows moderate evolution and the stellar mass density (rho_M) decreases, with both being always lower than the total rho_UV and rho_M of more typical galaxies but slowly approaching them with increasing redshift. Overall, our results indicate that both rho_UV and rho_M of LAEs slowly approach the measurements of continuum-selected galaxies at z>6, which suggests a key role of LAEs in the epoch of reionisation.
Aims. The aim of this work is to constrain the evolution of the fraction of Lya emitters among UV selected star forming galaxies at 2<z<6, and to measure the stellar escape fraction of Lya photons over the same redshift range. Methods. We exploit the ultradeep spectroscopic observations collected by the VIMOS Ultra Deep Survey (VUDS) to build an unique, complete and unbiased sample of 4000 spectroscopically confirmed star forming galaxies at 2<z<6. Our galaxy sample UV luminosities brighter than M* at 2<z<6, and luminosities down to one magnitude fainter than M* at 2<z<3.5. Results. We find that 80% of the star forming galaxies in our sample have EW0(Lya)<10A, and correspondingly fesc(Lya)<1%. By comparing these results with literature, we conclude that the bulk of the Lya luminosity at 2<z<6 comes from galaxies that are fainter in the UV than those we sample in this work. The strong Lya emitters constitute, at each redshift, the tail of the distribution of the galaxies with extreme EW0(Lya) and fesc(Lya) . This tail of large EW0 and fesc(Lya) becomes more important as the redshift increases, and causes the fraction of Lya with EW0> 25A to increase from 5% at z=2 to 30% at z=6, with the increase being relatively stronger beyond z=4. We observe no difference, for the narrow range of UV luminosities explored in this work, between the fraction of strong Lya emitters among galaxies fainter or brighter than M*, although the fraction for the FUV faint galaxies evolves faster, at 2<z<3.5, than for the bright ones. We do observe an anticorrelation between E(B-V) and fesc(Lya): generally galaxies with high fesc(Lya) have also small amounts of dust (and viceversa). However, when the dust content is low (E(B-V)<0.05) we observe a very broad range of fesc(Lya), ranging from 10^-3 to 1. This implies that the dust alone is not the only regulator of the amount of escaping Lya photons.
We present a clustering analysis of a sample of 238 Ly{$alpha$}-emitters at redshift 3<z<6 from the MUSE-Wide survey. This survey mosaics extragalactic legacy fields with 1h MUSE pointings to detect statistically relevant samples of emission line galaxies. We analysed the first year observations from MUSE-Wide making use of the clustering signal in the line-of-sight direction. This method relies on comparing pair-counts at close redshifts for a fixed transverse distance and thus exploits the full potential of the redshift range covered by our sample. A clear clustering signal with a correlation length of r0 = 2.9(+1.0/-1.1) Mpc (comoving) is detected. Whilst this result is based on only about a quarter of the full survey size, it already shows the immense potential of MUSE for efficiently observing and studying the clustering of Ly{$alpha$}-emitters.
We investigate the clustering and halo properties of $sim 5000$ Ly$alpha$-selected emission line galaxies (LAEs) from the Slicing COSMOS 4K (SC4K) and from archival NB497 imaging of SA22 split in 15 discrete redshift slices between $z sim 2.5 - 6$. We measure clustering lengths of $r_0 sim 3 - 6 h^{-1}$ Mpc and typical halo masses of $sim 10^{11}$ M$_odot$ for our narrowband-selected LAEs with typical $L_{rm{Ly}alpha} sim 10^{42 - 43}$ erg s$^{-1}$. The intermediate band-selected LAEs are observed to have $r_0 sim 3.5 - 15 h^{-1}$ Mpc with typical halo masses of $sim 10^{11 - 12}$ M$_odot$ and typical $L_{rm{Ly}alpha} sim 10^{43 - 43.6}$ erg s$^{-1}$. We find a strong, redshift-independent correlation between halo mass and Ly$alpha$ luminosity normalized by the characteristic Ly$alpha$ luminosity, $L^star(z)$. The faintest LAEs ($L sim 0.1 L^star(z)$) typically identified by deep narrowband surveys are found in $10^{10}$ M$_odot$ halos and the brightest LAEs ($L sim 7 L^star(z)$) are found in $sim 5 times 10^{12}$ M$_odot$ halos. A dependency on the rest-frame 1500 AA~UV luminosity, M$_rm{UV}$, is also observed where the halo masses increase from $10^{11}$ to $10^{13}$ M$_odot$ for M$_rm{UV} sim -19$ to $-23.5$ mag. Halo mass is also observed to increase from $10^{9.8}$ to $10^{12.3}$ M$_odot$ for dust-corrected UV star formation rates from $sim 0.6$ to $10$ M$_odot$ yr$^{-1}$ and continues to increase up to $10^{13.5}$ M$_odot$ in halo mass, where the majority of those sources are AGN. All the trends we observe are found to be redshift-independent. Our results reveal that LAEs are the likely progenitors of a wide range of galaxies depending on their luminosity, from dwarf-like, to Milky Way-type, to bright cluster galaxies. LAEs therefore provide unique insight into the early formation and evolution of the galaxies we observe in the local Universe.
Using the VLA and ALMA, we have obtained CO(2-1), [C II], [N II] line emission and multiple dust continuum measurements in a sample of normal galaxies at $z=5-6$. We report the highest redshift detection of low-$J$ CO emission from a Lyman Break Galaxy, at $zsim5.7$. The CO line luminosity implies a massive molecular gas reservoir of $(1.3pm0.3)(alpha_{rm CO}/4.5,M_odot$ (K km s$^{-1}$ pc$^2)^{-1})times10^{11},M_odot$, suggesting low star formation efficiency, with a gas depletion timescale of order $sim$1 Gyr. This efficiency is much lower than traditionally observed in $zgtrsim5$ starbursts, indicating that star forming conditions in Main Sequence galaxies at $zsim6$ may be comparable to those of normal galaxies probed up to $zsim3$ to-date, but with rising gas fractions across the entire redshift range. We also obtain a deep CO upper limit for a Main Sequence galaxy at $zsim5.3$ with $sim3$ times lower SFR, perhaps implying a high $alpha_{rm CO}$ conversion factor, as typically found in low metallicity galaxies. For a sample including both CO targets, we also find faint [N II] 205$,mu$m emission relative to [C II] in all but the most IR-luminous normal galaxies at $z=5-6$, implying more intense or harder radiation fields in the ionized gas relative to lower redshift. These radiation properties suggest that low metallicity may be common in typical $sim$10$^{10},M_odot$ galaxies at $z=5-6$. While a fraction of Main Sequence star formation in the first billion years may take place in conditions not dissimilar to lower redshift, lower metallicity may affect the remainder of the population.
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