ABSTRACT
We present
Hubble Space Telescope
F606W-band imaging observations of 21 galaxy-Ly
α
emitter lens candidates in the Baryon Oscillation Spectroscopic Survey Emission-Line Lens Survey (BELLS) ...for the GALaxy-Ly
α
EmitteR sYstems (BELLS GALLERY) survey. Seventeen systems are confirmed to be definite lenses with unambiguous evidence of multiple imaging. The lenses are primarily massive early-type galaxies (ETGs) at redshifts of approximately 0.55, while the lensed sources are Ly
α
emitters (LAEs) at redshifts from two to three. Although most of the lens systems are well fit by smooth lens models consisting of singular isothermal ellipsoids in an external shear field, a thorough exploration of dark substructures in the lens galaxies is required. The Einstein radii of the BELLS GALLERY lenses are, on average, 60% larger than those of the BELLS lenses because of the much higher source redshifts. This will allow for a detailed investigation of the radius evolution of the mass profile in ETGs. With the aid of the average ∼13× lensing magnification, the LAEs are frequently resolved into individual star-forming knots with a wide range of properties. They have characteristic sizes from less than 100 pc to several kiloparsecs, rest-frame far-UV apparent AB magnitudes from 29.6 to 24.2, and typical projected separations of 500 pc to 2 kpc.
Abstract
The Mg
ii
λλ
2796, 2803 doublet has been suggested as a useful indirect indicator for the escape of Ly
α
and Lyman continuum (LyC) photons in local star-forming galaxies. However, studies to ...date have focused on small samples of galaxies with strong Mg
ii
or strong LyC emission. Here, we present the first study of Mg
ii
to probe a large dynamic range of galaxy properties, using newly obtained high-signal-to-noise, moderate-resolution spectra of Mg
ii
, for a sample of 34 galaxies selected from the Low-redshift Lyman Continuum Survey. We show that the galaxies in our sample have Mg
ii
profiles ranging from strong emission to P-Cygni profiles to pure absorption. We find that there is a significant trend (with a possibility of spurious correlations of ∼2%) that galaxies that are detected as strong LyC emitters (LCEs) show larger equivalent widths of Mg
ii
emission, while non-LCEs tend to show evidence of more scattering and absorption features in Mg
ii
. We then find that Mg
ii
strongly correlates with Ly
α
in both equivalent width and escape fraction, regardless of whether emission or absorption dominates the Mg
ii
profiles. Furthermore, we show that, for galaxies that are categorized as Mg
ii
emitters, one can use the information of Mg
ii
, metallicity, and dust to estimate the escape fraction of LyC within a factor of ∼3. These findings confirm that Mg
ii
lines can be used as a tool for selecting galaxies as LCEs and thus serve as an indirect indicator for the escape of Ly
α
and LyC.
Abstract
We present a morphological study of the 17 lensed Ly
α
emitter (LAE) galaxies of the Baryon Oscillation Spectroscopic Survey Emission-Line Lens Survey (BELLS) for the GALaxy-Ly
α
EmitteR ...sYstems (BELLS GALLERY) sample. This analysis combines the magnification effect of strong galaxy–galaxy lensing with the high resolution of the
Hubble Space Telescope
to achieve a physical resolution of ∼80 pc for this 2 <
z
< 3 LAE sample, allowing a detailed characterization of the LAE rest-frame ultraviolet continuum surface brightness profiles and substructure. We use lens-model reconstructions of the LAEs to identify and model individual clumps, which we subsequently use to constrain the parameters of a generative statistical model of the LAE population. Since the BELLS GALLERY sample is selected primarily on the basis of Ly
α
emission, the LAEs that we study here are likely to be directly comparable to those selected in wide-field, narrowband LAE surveys, in contrast with the lensed LAEs identified in cluster-lensing fields. We find an LAE clumpiness fraction of approximately 88%, which is significantly higher than that found in previous (non-lensing) studies. We find a well-resolved characteristic clump half-light radii of ∼350 pc, a scale comparable to the largest H
ii
regions seen in the local universe. This statistical characterization of LAE surface-brightness profiles will be incorporated into future lensing analyses using the BELLS GALLERY sample to constrain the incidence of dark-matter substructure in the foreground lensing galaxies.
Abstract
We report the detection of ADFS-27, a dusty, starbursting major merger at a redshift of
z
= 5.655, using the Atacama Large Millimeter/submillimeter Array (ALMA). ADFS-27 was selected from
...Herschel
/Spectral and Photometric Imaging Receiver (SPIRE) and APEX/LABOCA data as an extremely red “870
μ
m riser” (i.e.,
), demonstrating the utility of this technique to identify some of the highest-redshift dusty galaxies. A scan of the 3 mm atmospheric window with ALMA yields detections of CO(
J
= 5 → 4) and CO(
J
= 6 → 5) emission, and a tentative detection of H
2
O(2
11
→ 2
02
) emission, which provides an unambiguous redshift measurement. The strength of the CO lines implies a large molecular gas reservoir with a mass of
M
gas
= 2.5 × 10
11
M
⊙
, sufficient to maintain its ∼2400
M
⊙
yr
−1
starburst for at least ∼100 Myr. The 870
μ
m dust continuum emission is resolved into two components, 1.8 and 2.1 kpc in diameter, separated by 9.0 kpc, with comparable dust luminosities, suggesting an ongoing major merger. The infrared luminosity of
L
IR
≃ 2.4 × 10
13
L
⊙
implies that this system represents a binary hyper-luminous infrared galaxy, the most distant of its kind presently known. This also implies star formation rate surface densities of
and 750
M
⊙
yr
−1
kpc
2
, consistent with a binary “maximum starburst.” The discovery of this rare system is consistent with a significantly higher space density than previously thought for the most luminous dusty starbursts within the first billion years of cosmic time, easing tensions regarding the space densities of
z
∼ 6 quasars and massive quiescent galaxies at
z
≳ 3.
The Low-Redshift Lyman Continuum Survey Saldana-Lopez, Alberto; Schaerer, Daniel; Chisholm, John ...
Astronomy and astrophysics (Berlin),
07/2022, Volume:
663
Journal Article
Peer reviewed
Open access
Aims.
Combining 66 ultraviolet (UV) spectra and ancillary data from the recent Low-Redshift Lyman Continuum Survey (LzLCS) and 23 LyC observations by earlier studies, we form a statistical sample of ...star-forming galaxies at
z
∼ 0.2 − 0.4 with which we study the role of cold interstellar medium (ISM) gas in the leakage of ionizing radiation. We also aim to establish empirical relations between the H
I
neutral and low-ionization state (LIS) absorption lines with different galaxy properties.
Methods.
We first constrain the massive star content (stellar ages and metallicities) and UV attenuation by fitting the stellar continuum with a combination of simple stellar population models. The models, together with accurate LyC flux measurements, allow us to determine the absolute LyC photon escape fraction for each galaxy (
f
esc
abs
). We then measure the equivalent widths and residual fluxes of multiple H
I
and LIS lines, and the geometrical covering fraction of the UV emission, adopting the picket-fence model.
Results.
The LyC escape fraction spans a wide range, with a median
f
esc
abs
(0.16, 0.84 quantiles) of 0.04 (0.02, 0.20), and 50 out of the 89 galaxies detected in the LyC (1
σ
upper limits of
f
esc
abs
≲ 0.01 for non-detections, typically). The H
I
and LIS line equivalent widths scale with the UV luminosity and attenuation, and inversely with the residual flux of these lines. Additionally, Ly
α
equivalent widths scale with both the H
I
and LIS residual fluxes, but anti-correlate with the corresponding H
I
or LIS equivalent widths. The H
I
and LIS residual fluxes are correlated, indicating that the neutral gas is spatially traced by the low-ionization transitions. We find that the observed trends of the absorption lines and the UV attenuation are primarily driven by the geometric covering fraction of the gas. The observed nonuniform gas coverage also demonstrates that LyC photons escape through low-column-density channels in the ISM. The equivalent widths and residual fluxes of both the H
I
and LIS lines strongly correlate with
f
esc
abs
: strong LyC leakers (highest
f
esc
abs
) show weak absorption lines, low UV attenuation, and large Ly
α
equivalent widths. We provide several empirical calibrations to estimate
f
esc
abs
from UV absorption lines. Finally, we show that simultaneous UV absorption line and dust attenuation measurements can, in general, predict the escape fraction of galaxies. We apply our method to available measurements of UV LIS lines of 15 star-forming galaxies at
z
∼ 4 − 6 (plus 3 high-
z
galaxy composites), finding that these high-redshift, UV-bright galaxies (
M
UV
≲ −21) may have low escape fractions,
f
esc
abs
≲ 0.1.
Conclusions.
UV absorption lines trace the cold ISM gas of galaxies, which governs the physics of the LyC escape. We show that, with some assumptions, the absolute LyC escape can be statistically predicted using UV absorption lines, and the method can be applied to study galaxies across a wide redshift range, including in the epoch of cosmic reionization.
ABSTRACT
We introduce the Baryon Oscillation Spectroscopic Survey (BOSS) Emission-Line Lens Survey GALaxy-Ly
α
EmitteR sYstems (BELLS GALLERY) Survey, which is a
Hubble Space Telescope
program to ...image a sample of galaxy-scale strong gravitational lens candidate systems with high-redshift Ly
α
emitters (LAEs) as the background sources. The goal of the BELLS GALLERY Survey is to illuminate dark substructures in galaxy-scale halos by exploiting the small-scale clumpiness of rest-frame far-UV emission in lensed LAEs, and to thereby constrain the slope and normalization of the substructure-mass function. In this paper, we describe in detail the spectroscopic strong-lens selection technique, which is based on methods adopted in the previous Sloan Lens ACS (SLACS) Survey, BELLS, and SLACS for the Masses Survey. We present the BELLS GALLERY sample of the 21 highest-quality galaxy–LAE candidates selected from
galaxy spectra in the BOSS of the Sloan Digital Sky Survey III. These systems consist of massive galaxies at redshifts of approximately 0.5 strongly lensing LAEs at redshifts from 2–3. The compact nature of LAEs makes them an ideal probe of dark substructures, with a substructure-mass sensitivity that is unprecedented in other optical strong-lens samples. The magnification effect from lensing will also reveal the structure of LAEs below 100 pc scales, providing a detailed look at the sites of the most concentrated unobscured star formation in the universe. The source code used for candidate selection is available for download as a part of this release.
ABSTRACT We report the discovery of SDSS J0909+4449, an exceptional system consisting of a quasar at z = 2.788 strongly lensed by a group of galaxies at z ∼ 0.9 into three images separated by up to ...14 arcsec based on archival data collected by the Sloan Digital Sky Survey, extended Baryon Oscillation Spectroscopic Survey, Beijing–Arizona Sky Survey, the Mayall z-band Legacy Survey, and the Gemini Telescope. We discuss two hypotheses on the nature of SDSS J0909+4449, i.e. a rare triply imaged quasar in the naked cusp configuration and a typical quadruply imaged quasar with the fourth image undetected in this data. We find that simple lens models can provide excellent fits to the observed image positions and the non-detection under either hypothesis. Deeper imaging data, spectroscopic observations, and follow-up light-curve measurements will be helpful in determining which hypothesis is correct and provide better constraints on the lens mass distribution. Nevertheless, given its unusually large image separations, SDSS J0909+4449 will be a unique probe for the mass structure and the underlying cooling and stellar feedback processes on group or cluster scales.
Abstract
Star-forming galaxies are considered the likeliest source of the H
i
ionizing Lyman continuum (LyC) photons that reionized the intergalactic medium at high redshifts. However, above
z
≳ 6, ...the neutral intergalactic medium prevents direct observations of LyC. Therefore, recent years have seen the development of
indirect
indicators for LyC that can be calibrated at lower redshifts and applied in the epoch of reionization. Emission from the Mg
ii
λλ
2796, 2803 doublet has been proposed as a promising LyC proxy. In this paper, we present new Hubble Space Telescope/Cosmic Origins Spectrograph observations for eight LyC emitter candidates, selected to have strong Mg
ii
emission lines. We securely detect LyC emission in 50% (4/8) of the galaxies with 2
σ
significance. This high detection rate suggests that strong Mg
ii
emitters might be more likely to leak LyC than similar galaxies without strong Mg
ii
. Using photoionization models, we constrain the escape fraction of Mg
ii
as ∼15%–60%. We confirm that the escape fraction of Mg
ii
correlates tightly with that of Ly
α
, which we interpret as an indication that the escape fraction of both species is controlled by resonant scattering in the same low column density gas. Furthermore, we show that the combination of the Mg
ii
emission and dust attenuation can be used to estimate the escape fraction of LyC statistically. These findings confirm that Mg
ii
emission can be adopted to estimate the escape fraction of Ly
α
and LyC in local star-forming galaxies and may serve as a useful indirect indicator at the epoch of reionization.
Sources that leak Lyman continuum (LyC) photons and lead to the reionisation of the universe are an object of intense study using multiple observing facilities. Recently the Low-redshift LyC Survey ...(LzLCS) has presented the first large sample of LyC emitting galaxies at low redshift ($z 0.3$) with the Hubble Space Telescope Cosmic Origins Spectrograph . The LzLCS sample contains a robust estimate of the LyC escape fraction ( ) for 66 galaxies, spanning a wide range of values. Here, we aim to study the dependence of on the radio continuum (RC) properties of LzLCS sources. Overall, RC emission can provide unique insights into the role of supernova feedback, cosmic rays (CRs), and magnetic fields from its non-thermal emission component. RC emission is also a dust-free tracer of the star formation rate (SFR) in galaxies. In this study, we present Karl G. Jansky Very Large Array (VLA) RC observations of the LzLCS sources at gigahertz (GHz) frequencies. We performed VLA C (4-8 GHz) and S (2-4 GHz) band observations for a sample of 53 LzLCS sources. We also observed a sub-sample of 17 LzLCS sources in the L (1-2 GHz) band. We detected RC from both C- and S-bands in 24 sources for which we are able to estimate their radio spectral index across 3-6 GHz, denoted as . We also used the RC luminosity to estimate their SFRs. The radio spectral index of LzLCS sources spans a wide range, from flat ( $ -0.1$) to very steep ($ -1.0$). They have a steeper mean -0.92$) compared to that expected for normal star-forming galaxies ( -0.64$). They also show a larger scatter in (sim 0.71) compared to that of normal star-forming galaxies (sim 0.15). The strongest leakers in our sample show flat weak leakers have close to normal star-forming galaxies and non-leakers are characterized by steep . We argue that a combination of young ages, free-free absorption, and a flat cosmic-ray energy spectrum can altogether lead to a flat for strong leakers. Non-leakers are characterized by steep spectra which can arise due to break or cutoff at high frequencies. Such a cutoff in the spectrum can arise in a single injection model of CRs characteristic of galaxies which have recently stopped star-formation. The dependence of on (which is orientation-independent) suggests that the escape of LyC photons is not highly direction-dependent at least to the first order. The radio-based SFRs ( ) of LzLCS sources show a large offset ($ dex) from the standard calibration. We find that adding as a second parameter helps us to calibrate the with and within a scatter of $ dex. For the first time, we have found a relation between and . This hints at the interesting role of supernovae feedback, CRs, and magnetic fields in facilitating the escape (alternatively, and/or the lack) of LyC photons.
The geometry of the neutral gas in and around galaxies is a key regulator of the escape of ionizing photons. We present the first statistical study aimed at linking the neutral and ionized gas ...distributions to the Lyman continuum (LyC) escape fraction ( f esc LyC ) in a sample of 22 confirmed LyC leakers and non-leakers at z ≈ 0.35 using the Keck Cosmic Web Imager (Keck/KCWI) and the Low Resolution Spectrograph 2 (HET/LRS2). Our integral field unit data enable the detection of neutral and low-ionization gas, as traced by Mg II , and ionized gas, as traced by O II , extending beyond the stellar continuum for seven and ten objects, respectively. All but one object with extended Mg II emission also show extended O II emission; in this case, Mg II emission is always more extended than O II by a factor 1.2 on average. Most of the galaxies with extended emission are non or weak LyC leakers ( f esc LyC < 5%), but we find a large diversity of neutral and low-ionization gas configurations around these weakly LyC-emitting galaxies. Conversely, the strongest leakers ( f esc LyC > 5%) appear uniformly compact in both Mg II and O II with exponential scale lengths ≲1 kpc. Most are unresolved at the resolution of our data. We also find a trend between f esc LyC and the spatial offsets of the nebular gas and the stellar continuum emission. Moreover, we find significant anticorrelations between the spatial extent of the neutral and/or low-ionization gas and the O III /O II ratio, and H β equivalent width, as well as positive correlations with metallicity and UV size, suggesting that galaxies with more compact neutral and/or low-ionization gas sizes are more highly ionized. The observations suggest that strong LyC emitters do not have extended neutral and/or low-ionization gas halos and ionizing photons may be emitted in many directions. Combined with high ionization diagnostics, we propose that the Mg II , and potentially O II , spatial compactness are indirect indicators of LyC emitting galaxies at high redshift.
PDF
