Exploring the Correlation between Hα\rm{H}\alpha-to-UV Ratio and Burstiness for Typical Star-forming Galaxies at z∼2z\sim2

The $\rm{H}\alpha$-to-UV luminosity ratio ($L(\rm H\alpha)/L(\rm UV)$) is often used to probe SFHs of star-forming galaxies and it is important to validate it against other proxies for burstiness. To address this issue, we present a statistical analysis of the resolved distribution of $\Sigma_{\rm{SFR}}$ as well as stellar age and their correlations with the globally measured $L(\rm H\alpha)/L(\rm UV)$ for a sample of 310 star-forming galaxies in two redshift bins of $1.37 < z < 1.70$ and $2.09 < z < 2.61$ observed by the MOSDEF survey. We use the multi-waveband CANDELS/3D-HST imaging of MOSDEF galaxies to construct $\Sigma_{\rm{SFR}}$ and stellar age maps. We analyze the composite rest-frame far-UV spectra of a subsample of MOSDEF targets obtained by the Keck/LRIS, which includes 124 star-forming galaxies (MOSDEF-LRIS) at redshifts $1.4 < z < 2.6$, to examine the average stellar population properties, and the strength of age-sensitive FUV spectral features in bins of $L(\rm H\alpha)/L(\rm UV)$. Our results show no significant evidence that individual galaxies with higher $L(\rm H\alpha)/L(\rm UV)$ are undergoing a burst of star formation based on the resolved distribution of $\Sigma_{\rm{SFR}}$ of individual star-forming galaxies. We segregate the sample into subsets with low and high $L(\rm H\alpha)/L(\rm UV)$. The high-$L(\rm H\alpha)/L(\rm UV)$ subset exhibits, on average, an age of $\log[\rm{Age/yr}]$ = 8.0, compared to $\log[\rm{Age/yr}]$ = 8.4 for the low-$L(\rm H\alpha)/L(\rm UV)$ galaxies, though the difference in age is significant at only the $2\sigma$ level. Furthermore, we find no variation in the strengths of Siiv$\lambda\lambda1393, 1402$ and Civ$\lambda\lambda1548, 1550$ P-Cygni features from massive stars between the two subsamples.Comment: 16 pages, 10 figures, published by the Monthly Notices of the Royal Astronomical Societ

The clustering of typical Lyαα emitters from z∼2.5−6z \sim 2.5 - 6: host halo masses depend on Lyαα and UV luminosities

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

The evolution of the UV luminosity and stellar mass functions of Lyman-alpha emitters from z~2 to z~6

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

The production and escape of Lyman-Continuum radiation from star-forming galaxies at z ∼ 2 and their redshift evolution

We study the production and escape of ionizing photons of a sample of 588 H$\alpha$ (Ha) emitters (HAEs) at z=2.2 in COSMOS by exploring their rest-frame Lyman Continuum (LyC) with GALEX/NUV data. We find 8 candidate LyC leakers with f$_{esc}$>60% out of a clean subsample of 191 HAEs (i.e. without any neighbour or foreground galaxy inside the GALEX PSF). Overall, we measure a very low escape fraction f$_{esc}$

A comprehensive study of Hα\alpha emitters at z∼z \sim 0.62 in the DAWN survey: the need for deep and wide regions

We present new estimates of the luminosity function (LF) and star formation rate density (SFRD) for an H$\alpha$ selected sample at $z\sim0.62$ from the Deep And Wide Narrow-band (DAWN) survey. Our results are based on a new H$\alpha$ sample in the extended COSMOS region (compared to Coughlin et al. 2018) with the inclusion of flanking fields, resulting in a total area coverage of $\sim$1.5 deg$^2$. A total of 241 H$\alpha$ emitters were selected based on robust selection criteria using spectro-photometric redshifts and broadband color-color classification. We explore the effect of different dust correction prescriptions by calculating the LF and SFRD using a constant dust extinction correction, A{$_{\textrm{H}\alpha}=1$} mag, a luminosity-dependent correction, and a stellar-mass dependent correction. The resulting H$\alpha$ LFs are well fitted using Schechter functions with best-fit parameters: L$^*=10^{42.24}$ erg s$^{-1}$, $\phi^*=10^{-2.85}$ Mpc$^{-3}$, $\alpha = -1.62$ for constant dust correction, L$^*=10^{42.31}$ erg s$^{-1}$, $\phi^*=10^{-2.8}$ Mpc$^{-3}$, $\alpha=-1.39$ for luminosity-dependent dust correction, and L$^*=10^{42.36}$ erg s$^{-1}$, $\phi^*=10^{-2.91}$ Mpc$^{-3}$, $\alpha = -1.48$, for stellar mass-dependent dust correction. The deep and wide nature of the DAWN survey effectively samples H$\alpha$ emitters over a wide range of luminosities, thereby providing better constraints on both the faint and bright end of the LF. Also, the SFRD estimates $\rho_{\textrm{SFR}}=10^{-1.39}$ M$_{\odot}$yr$^{-1}$Mpc$^{-3}$ (constant dust correction), $\rho_{\textrm{SFR}}=10^{-1.47}$ M$_{\odot}$yr$^{-1}$Mpc$^{-3}$ (luminosity-dependent dust correction), and $\rho_{\textrm{SFR}}=10^{-1.49}$ M$_{\odot}$yr$^{-1}$Mpc$^{-3}$ (stellar mass-dependent dust correction) are in good agreement with the evolution of SFRD across redshifts ($0 < z < 2$) seen from previous H$\alpha$ surveys.Comment: 16 pages, 8 figures, Accepted for publication in Ap

The Evolution of Star-Forming Galaxies Using the Largest Narrowband Surveys

Observations of the star formation history of the Universe shows that galaxies have evolved considerably over the past 13 Gyrs, but what is causing such an evolution to occur? To answer this question is to delve deeper and ask more fundamental questions: How are the statistical properties of galaxies changing with time? What mechanisms/drivers are involved? How does the host halo influence the residing galaxy’s evolution? What are the progenitors of the present-day galaxies?To address these questions, I use unique, narrowband selected samples of 3475 Hβ+[Oiii]- and 3298 [Oii]-selected emission line galaxies from the High-z Emission Line Survey (HiZELS) and ∼ 4000 Lyα-selected galaxies from the Slicing COSMOS 4K (SC4K) survey. The HiZELS survey covers samples divided in four discrete redshift slices (∆z ∼ 0.01 − 0.03) between z ∼ 0.8 − 3.3 and z ∼ 1.5 − 5 for Hβ+[Oiii] and [Oii] emitters, respectively, and the SC4K covers Lyα samples divided in 15 discrete redshift slices (∆z ∼ 0.02 − 0.15) between z ∼ 2.5 − 6.Measurements of the [Oiii] and [Oii] stellar mass and luminosity functions are presented for the first time up to z ∼ 3 and 5, respectively. Both [Oiii] and [Oii] emitters show stellar mass and luminosity functions that strongly evolve with redshift with [Oii] emitters observed to become rarer with increasing redshift. I present measurements of the star formation history of the Universe using only [Oii] from the local Universe to z ∼ 5. I confirm that star formation rates strongly increase from z ∼ 5 to a peak around z ∼ 3 and gradually decrease to the present-day. Stellar mass densities of [Oiii] and [Oii] emitters are found to trace the stellar mass buildup of star-forming galaxies, but diverge at z &lt; 1 from the global population of galaxies, suggesting a decreasing fraction of star forming galaxies due to quenching mechanisms.I investigate the evolution of the equivalent widths of Hα, [Oiii], and [Oii] emitters and find different evolutions for both lines. Hα and [Oiii] emitters are found to continuously increase with redshift, while [Oii] equivalent widths increase up to z ∼ 4 and decrease quickly at higher redshifts. Comparing the evolution of the [Oiii] and [Oii] equivalent widths suggests an increasingly energetic ionization state of the gas in the interstellar medium of star-forming galaxies. This explains the rapid drop in number densities of [Oii] emitters in respect to [Oiii]-selected emitters where due to higher [Oiii]/[Oii] line ratios, [Oii] emitters become increasingly rare due to changes in the physical conditions of the interstellar medium.I conclude my work by investigating the clustering and halo properties of [Oiii], [Oii], and Lyα emitters. Strong evolutions in the clustering lengths for all redshift samples is observed with galaxies being more clustered at higher redshifts. Applying models to convert clustering lengths to halo masses shows that galaxy properties and halo masses are tightly correlated with one another. Strong, redshift-independent trends between halo mass and line luminosity, stellar mass, rest-frame 1500 ̊A luminosity, and UV star formation rate are observed. This signifies the important role that halos play in the overall evolution of star-forming galaxies. Lastly, I find that Lyα emitters at high-z are progenitors of a wide range of present-day galaxies, ranging from dwarf-like, to Milky Way, to large cluster galaxies making them ideal tools to study the formation of galaxies in the local Universe

The Evolution of Star-Forming Galaxies Using the Largest Narrowband Surveys

Observations of the star formation history of the Universe shows that galaxies have evolved considerably over the past 13 Gyrs, but what is causing such an evolution to occur? To answer this question is to delve deeper and ask more fundamental questions: How are the statistical properties of galaxies changing with time? What mechanisms/drivers are involved? How does the host halo influence the residing galaxy’s evolution? What are the progenitors of the present-day galaxies?To address these questions, I use unique, narrowband selected samples of 3475 Hβ+[Oiii]- and 3298 [Oii]-selected emission line galaxies from the High-z Emission Line Survey (HiZELS) and ∼ 4000 Lyα-selected galaxies from the Slicing COSMOS 4K (SC4K) survey. The HiZELS survey covers samples divided in four discrete redshift slices (∆z ∼ 0.01 − 0.03) between z ∼ 0.8 − 3.3 and z ∼ 1.5 − 5 for Hβ+[Oiii] and [Oii] emitters, respectively, and the SC4K covers Lyα samples divided in 15 discrete redshift slices (∆z ∼ 0.02 − 0.15) between z ∼ 2.5 − 6.Measurements of the [Oiii] and [Oii] stellar mass and luminosity functions are presented for the first time up to z ∼ 3 and 5, respectively. Both [Oiii] and [Oii] emitters show stellar mass and luminosity functions that strongly evolve with redshift with [Oii] emitters observed to become rarer with increasing redshift. I present measurements of the star formation history of the Universe using only [Oii] from the local Universe to z ∼ 5. I confirm that star formation rates strongly increase from z ∼ 5 to a peak around z ∼ 3 and gradually decrease to the present-day. Stellar mass densities of [Oiii] and [Oii] emitters are found to trace the stellar mass buildup of star-forming galaxies, but diverge at z &lt; 1 from the global population of galaxies, suggesting a decreasing fraction of star forming galaxies due to quenching mechanisms.I investigate the evolution of the equivalent widths of Hα, [Oiii], and [Oii] emitters and find different evolutions for both lines. Hα and [Oiii] emitters are found to continuously increase with redshift, while [Oii] equivalent widths increase up to z ∼ 4 and decrease quickly at higher redshifts. Comparing the evolution of the [Oiii] and [Oii] equivalent widths suggests an increasingly energetic ionization state of the gas in the interstellar medium of star-forming galaxies. This explains the rapid drop in number densities of [Oii] emitters in respect to [Oiii]-selected emitters where due to higher [Oiii]/[Oii] line ratios, [Oii] emitters become increasingly rare due to changes in the physical conditions of the interstellar medium.I conclude my work by investigating the clustering and halo properties of [Oiii], [Oii], and Lyα emitters. Strong evolutions in the clustering lengths for all redshift samples is observed with galaxies being more clustered at higher redshifts. Applying models to convert clustering lengths to halo masses shows that galaxy properties and halo masses are tightly correlated with one another. Strong, redshift-independent trends between halo mass and line luminosity, stellar mass, rest-frame 1500 ̊A luminosity, and UV star formation rate are observed. This signifies the important role that halos play in the overall evolution of star-forming galaxies. Lastly, I find that Lyα emitters at high-z are progenitors of a wide range of present-day galaxies, ranging from dwarf-like, to Milky Way, to large cluster galaxies making them ideal tools to study the formation of galaxies in the local Universe