Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userComplex Lyman Alpha Profiles in Redshift 6.6 Ultraluminous Lyman Alpha Emitters
92
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report on a search for ultraluminous Lyman alpha emitting galaxies (LAEs) at z=6.6 using the NB921 filter on Hyper Suprime-Cam on the Subaru telescope. We searched a 30 degree squared area around the North Ecliptic Pole, which we observed in broadband g, r, i, z, and y and narrowband NB816 and NB921, for sources with NB921 < 23.5 and z - NB921 > 1.3. This corresponds to a selection of log L(Ly-alpha) > 43.5 erg/s. We followed up seven candidate LAEs (out of thirteen) with the Keck DEIMOS spectrograph and confirmed five z=6.6 LAEs, one z=6.6 AGN with a broad Ly-alpha line and a strong red continuum, and one low-redshift ([OIII]5007) galaxy. The five ultraluminous LAEs have wider line profiles than lower luminosity LAEs, and one source, NEPLA4, has a complex line profile similar to that of COLA1. In combination with previous results, we show that the line profiles of the z=6.6 ultraluminous LAEs are systematically different than those of lower luminosity LAEs at this redshift. This result suggests that ultraluminous LAEs generate highly ionized regions of the intergalactic medium in their vicinity that allow the full Lyman alpha profile of the galaxy---including any blue wings---to be visible. If this interpretation is correct, then ultraluminous LAEs offer a unique opportunity to determine the properties of the ionized zones around them, which will help in understanding the ionization of the z ~ 7 intergalactic medium. A simple calculation gives a very rough estimate of 0.015 for the escape fraction of ionizing photons, but more sophisticated calculations are needed to fully characterize the uncertainties.
rate research
Read More
We report the detection of the most luminous high-redshift Lyman Alpha Emitting galaxy (LAE) yet seen, with log L(Ly alpha) = 43.9 ergs/s. The galaxy -- COSMOS Lyman alpha 1, or COLA1 -- was detected in a search for ultra-luminous LAEs with Hyper Suprime-Cam on the Subaru telescope. It was confirmed to lie at z = 6.593 based on a Lyman alpha line detection obtained from followup spectroscopy with the DEIMOS spectrograph on Keck2. COLA1 is the first very high-redshift LAE to show a multi-component Lyman alpha line profile with a blue wing, which suggests that it could lie in a highly ionized region of the intergalactic medium and could have significant infall. If this interpretation is correct, then ultra-luminous LAEs like COLA1 offer a unique opportunity to determine the properties of the HII regions around these galaxies which will help in understanding the ionization of the z ~ 7 intergalactic medium.
We present the luminosity function (LF) for ultraluminous Ly$alpha$ emitting galaxies (LAEs) at z = 6.6. We define ultraluminous LAEs (ULLAEs) as galaxies with logL(Ly$alpha$) > 43.5 erg s$^{-1}$. We select our main sample using the g, r, i, z, and NB921 observations of a wide-area (30 deg$^2$) Hyper Suprime-Cam survey of the North Ecliptic Pole (NEP) field. We select candidates with g, r, i > 26, NB921 $leq$ 23.5, and NB921 - z $leq$ 1.3. Using the DEIMOS spectrograph on Keck II, we confirm 9 of our 14 candidates as ULLAEs at z = 6.6 and the remaining 5 as an AGN at z = 6.6, two [OIII]$lambda$5007 emitting galaxies at z = 0.84 and z = 0.85, and two non-detections. This emphasizes the need for full spectroscopic follow-up to determine accurate LFs. In constructing the ULLAE LF at z = 6.6, we combine our 9 NEP ULLAEs with two previously discovered and confirmed ULLAEs in the COSMOS field: CR7 and COLA1. We apply rigorous corrections for incompleteness based on simulations. We compare our ULLAE LF at z = 6.6 with LFs at z = 5.7 and z = 6.6 from the literature. Our data reject some previous LF normalizations and power law indices, but they are broadly consistent with others. Indeed, a comparative analysis of the different literature LFs suggests that none is fully consistent with any of the others, making it critical to determine the evolution from z = 5.7 to z = 6.6 using LFs constructed in exactly the same way at both redshifts.
We study six luminous Lyman-alpha emitters (LAEs) with very blue rest-frame UV continua at $5.7le z le 6.6$. These LAEs have previous HST and Spitzer IRAC observations. Combining our newly acquired HST images, we find that their UV-continuum slopes $beta$ are in a range of $-3.4le beta le -2.6$. Unlike previous, tentative detections of $beta simeq -3$ in photometrically selected, low-luminosity galaxies, our LAEs are spectroscopically confirmed and luminous ($M_{rm UV}<-20$ mag). We model their broadband spectral energy distributions (SEDs), and find that two $betasimeq-2.6pm0.2$ galaxies can be well fitted with young and dust-free stellar populations. However, it becomes increasingly difficult to fit bluer galaxies. We explore further interpretations by including non-zero LyC escape fraction $f_{rm esc}$, very low metallicities, and/or AGN contributions. Assuming $f_{rm esc}simeq0.2$, we achieve the bluest slopes $betasimeq-2.7$ when nebular emission is considered. This can nearly explain the SEDs of two galaxies with $betasimeq-2.8$ and --2.9 ($sigma_{beta}=0.15$). Larger $f_{rm esc}$ values and very low metallicities are not favored by the strong nebular line emission (evidenced by the IRAC flux) or the observed (IRAC 1 - IRAC 2) color. Finally, we find that the $betasimeq-2.9$ galaxy can potentially be well explained by the combination of a very young population with a high $f_{rm esc}$ ($ge0.5$) and an old, dusty population. We are not able to produce two $beta simeq -3.4 pm0.4$ galaxies. Future deep spectroscopic observations are needed to fully understand these galaxies.
This publication contains the conference summary of the Understanding Lyman-alpha Emitters conference held at the Max Planck Institute for Astronomy in Heidelberg October 6 - 10, 2008. The scope of the conference was to bring together most of the scientists working in the field of Lyman-alpha emitters, whether at low or high redshift, or on observational or theoretical aspects, and to summarise how far the field of study of galaxies with Lyman-alpha emission has come. An outlook towards the future of the field was also desired. As part of the conference, two days were dedicated to in total six discussion sessions. The topics were i) new methods and selection methods, ii) morphology, iii) what can the local Universe observations tell us about the high redshift Universe?, iv) clustering, v) SED fitting and vi) Ly-alpha blobs. The chairs of those sessions were asked to summarise the discussions, as presented in these proceedings.
Identifying the mechanisms driving the escape of Lyman Continuum (LyC) photons is crucial to find Lyman Continuum Emitter (LCE) candidates. To understand the physical properties involved in the leakage of LyC photons, we investigate the connection between the HI covering fraction, HI velocity width, the Lyman alpha (LyA) properties and escape of LyC photons in a sample of 22 star-forming galaxies including 13 LCEs. We fit the stellar continua, dust attenuation, and absorption lines between 920 and 1300 A to extract the HI covering fractions and dust attenuation. Additionally, we measure the HI velocity widths of the optically thick Lyman series and derive the LyA equivalent widths (EW), escape fractions (fesc), peak velocities and fluxes at the minimum of the LyA profiles. Overall, we highlight strong correlations between the presence of low HI covering fractions and (1) low LyA peak velocities; (2) more flux at the profile minimum; and (3) larger EW(LyA), fesc(LyA), and fesc(LyC). Hence, low column density channels are crucial ISM ingredients for the leakage of LyC and LyA photons. Additionally, galaxies with narrower HI absorption velocity widths have higher LyA equivalent widths, larger LyA escape fractions, and lower LyA peak velocity separations. This suggests that these galaxies have low HI column density. Finally, we find that dust regulates the amount of LyA and LyC radiation that actually escapes the ISM. Overall, the ISM porosity is one origin of strong LyA emission and enables the escape of ionizing photons in low-z leakers. However, this is not enough to explain the largest fesc(LyC) observed, which indicates that the most extreme LCEs are likely density-bounded along all lines of sight to the observer. Overall, the neutral gas porosity constrains a lower limit to the escape fraction of LyC and LyA photons, providing a key estimator of the leakage of ionizing photons.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
