scholarly journals The VANDELS survey: a strong correlation between Ly α equivalent width and stellar metallicity at 3 ≤ z ≤ 5

2020 ◽  
Vol 495 (1) ◽  
pp. 1501-1510 ◽  
Author(s):  
F Cullen ◽  
R J McLure ◽  
J S Dunlop ◽  
A C Carnall ◽  
D J McLeod ◽  
...  
Keyword(s):  
Equivalent Width ◽  
Rest Frame ◽  
Star Forming ◽  
Lyman Alpha ◽  
Spectral Fitting ◽  
Best Fitting ◽  
Lyman Alpha Emitters ◽  
Galaxy Population ◽  
Far Ultraviolet ◽  
The Relationship

ABSTRACT We present the results of a new study investigating the relationship between observed Ly α equivalent width (Wλ(Ly α)) and the metallicity of the ionizing stellar population ( Z⋆) for a sample of 768 star-forming galaxies at 3 ≤ z ≤ 5 drawn from the VANDELS survey. Dividing our sample into quartiles of rest-frame Wλ(Ly α) across the range $-58 \,\rm {\mathring{\rm A}} \lesssim$Wλ(Ly α) $\lesssim 110 \,\rm {\mathring{\rm A}}$, we determine  Z⋆ from full spectral fitting of composite far-ultraviolet spectra and find a clear anticorrelation between Wλ(Ly α) and  Z⋆. Our results indicate that  Z⋆ decreases by a factor ≳ 3 between the lowest Wλ(Ly α) quartile (〈Wλ(Ly α)$\rangle =-18\,\rm {\mathring{\rm A}}$) and the highest Wλ(Ly α) quartile (〈Wλ(Ly α)$\rangle =24\,\rm {\mathring{\rm A}}$). Similarly, galaxies typically defined as Lyman alpha emitters (LAEs; Wλ(Ly α) $\gt 20\,\rm {\mathring{\rm A}}$) are, on average, metal poor with respect to the non-LAE galaxy population (Wλ(Ly α) $\le 20\,\rm {\mathring{\rm A}}$) with  Z⋆non-LAE ≳ 2 ×  Z⋆LAE. Finally, based on the best-fitting stellar models, we estimate that the increasing strength of the stellar ionizing spectrum towards lower  Z⋆ is responsible for ${\simeq}15{-}25{{\ \rm per\ cent}}$ of the observed variation in Wλ(Ly α) across our sample, with the remaining contribution (${\simeq}75{-}85{{\ \rm per\ cent}}$) being due to a decrease in the H i/dust covering fractions in low- Z⋆ galaxies.

Census of Lyα, [OIII]5007, Hα, and [CII]158μm Line Emission with ~1000 Low-mass Lyman Alpha Emitters at z = 4.9 – 7.0 Revealed with Subaru/Hyper-Suprime Cam Survey

2018 ◽  
Vol 14 (S344) ◽  
pp. 449-452
Author(s):  
Yuichi Harikane
Keyword(s):  
Equivalent Width ◽  
Rest Frame ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Line Emission ◽  
Flux Ratio ◽  
Lyman Alpha ◽  
Low Mass ◽  
Lyman Alpha Emitters ◽  
Turn Over

AbstractWe investigate Lyα, [Oiii] λ5007, Hα, and [Cii]158µm emission from 1,124 low-mass galaxies (typically M* ~ 108 Mʘ) at z = 4.9 - 7.0, composed of 1,092 Lyα emitters (LAEs) at z = 4.9 - 7.0 identified by Subaru/Hyper Suprime-Cam (HSC) narrowband surveys and 34 galaxies at z = 5.148 - 7.508 with deep ALMA [Cii]158µm data in the literature. At z = 4.9, we find that the rest-frame Hα equivalent width positively correlates with the rest-frame Lyα equivalent width EW0Lyα. At z = 5.7 - 7.0, there exists an interesting turn-over trend that the [ Oiii]/ Hα flux ratio increases in EW0Lyα ≃ 0 - 30 Å, and then decreases out to EW0Lyα ≃ 130 Å. We also identify an anti-correlation between a [ Cii] luminosity to star-formation rate ratio (L[CII]/SFR) and EW0Lyα at the >99% confidence level. We carefully investigate physical origins of the correlations, and find that a simple anti-correlation between EW0Lyα and metallicity explains self-consistently all of the relations identified in our study.

scholarly journals Lyman continuum escape fraction in Ly α emitters at z ≃ 3.1

2020 ◽  
Vol 493 (1) ◽  
pp. L65-L69 ◽  
Author(s):  
Fuyan Bian ◽  
Xiaohui Fan
Keyword(s):  
Equivalent Width ◽  
Rest Frame ◽  
Dwarf Galaxies ◽  
Stellar Mass ◽  
Lyman Alpha ◽  
Alpha Emitters ◽  
Upper Limit ◽  
Lyman Continuum ◽  
Lyman Alpha Emitters ◽  
The Universe

ABSTRACT We measure the Lyman continuum (LyC) escape fraction in 54 faint Lyman-alpha emitters (LAEs) at $z$ ≃ 3.1 in the GOODS-South field. With the average magnitude of R = 26.7 AB (MUV = −18.8 and L ≃ 0.1L*), these galaxies represent a population of compact young dwarf galaxies. Their properties are likely to resemble those in the galaxies responsible for reionizing the Universe at $z$ > 6. We do not detect LyC emission in any individual LAEs in the deep HST F336W images, which covers the rest-frame 820 Å. We do not detect the LyC emission of these LAEs in the stacked F336W images either. The 3σ upper limit of LyC escape fractions is $f_{\rm esc}\lt 14\!-\!32{{\ \rm per\ cent}}$. However, the high Ly α rest-frame equivalent width (EW), low stellar mass, and UV luminosity of these LAEs suggest that they should have $f_{\rm esc}\gt 50{{\ \rm per\ cent}}$. The low LyC escape fraction from this work and other stacking analyses suggests that the LyC-leaking galaxies with $f_{\rm esc}\gt 50{{\ \rm per\ cent}}$ at $z$ = 2–3 do not follow the relation between fesc and UV luminosity and Ly α EW derived from typical galaxies at similar redshifts. Therefore, the UV luminosity and Ly α EW are not the best indicators for the LyC escape fraction.

scholarly journals Unveiling the nature of the brightest z > 6 galaxies with ALMA and JWST

2019 ◽  
Vol 15 (S352) ◽  
pp. 20-20
Author(s):  
Rebecca Bowler
Keyword(s):  
Star Formation ◽  
Rest Frame ◽  
Small Samples ◽  
Star Forming ◽  
Lyman Alpha ◽  
Alpha Emission ◽  
Formation Conditions ◽  
Formation And Evolution ◽  
Insight Into

AbstractThe very brightest z > 6 galaxies are ideal laboratories for studying the physical properties of star-forming objects into the epoch of reionization. Selected from degree-scale, ground-based fields, these rare objects provide a key insight into early dust production and may harbour faint AGN. Targeted follow-up of small samples have unexpectedly shown both Lyman-alpha emission and other rest-frame UV lines (e.g CIV and HeII), suggesting unique star-formation conditions (or AGN) at early times. Furthermore, ALMA observations have revealed that 75% of the star-formation in these galaxies may be obscured. I will talk about HST/ALMA follow-up of bright z ∼ 7 LBGs in COSMOS and present new results from even brighter samples from z = 6 – 9 selected over ∼ 5 deg2. The power of both ALMA and JWST, coupled with the intrinsic luminosity of these sources, will provide a unique insight into the formation and evolution of vigorously star-forming galaxies in the first billion years.

scholarly journals Upper limits on the escape fraction of ionizing radiation from galaxies at 2 ≲ z < 6

2021 ◽  
Author(s):  
U Meštrić ◽  
E V Ryan-Weber ◽  
J Cooke ◽  
R Bassett ◽  
L J Prichard ◽  
...  
Keyword(s):  
Ionizing Radiation ◽  
Equivalent Width ◽  
Density Ratio ◽  
Groups Of Galaxies ◽  
Lyman Alpha ◽  
Alpha Emitters ◽  
Upper Limit ◽  
Lyman Continuum ◽  
Upper Limits ◽  
Lyman Alpha Emitters

Abstract In this work, we investigate upper limits on the global escape fraction of ionizing photons ($f_{\rm esc/global}^{\rm abs}$) from a sample of galaxies probed for Lyman-continuum (LyC) emission characterized as non-LyC and LyC leakers. We present a sample of 9 clean non-contaminated (by low redshift interlopers, CCD problems and internal reflections of the instrument) galaxies which do not show significant (&gt; 3σ) LyC flux between 880Å &lt;λrest &lt; 910Å. The 9 galaxy stacked spectrum reveals no significant LyC flux with an upper limit of $f_{\rm esc}^{\rm abs} \le 0.06$. In the next step of our analysis, we join all estimates of $f_{\rm esc}^{\rm abs}$ upper limits derived from different samples of 2 ≲ z &lt; 6 galaxies from the literature reported in last ∼20 years and include the sample presented in this work. We find the $f_{\rm esc}^{\rm abs}$ upper limit ≤ 0.084 for the galaxies recognized as non-LyC leakers. After including all known detections from literature $f_{\rm esc/global}^{\rm abs}$ upper limit ≤ 0.088 for all galaxies examined for LyC flux. Furthermore, $f_{\rm esc}^{\rm abs}$ upper limits for different groups of galaxies indicate that the strongest LyC emitters could be galaxies classified as Lyman alpha emitters. We also discuss the possible existence of a correlation among the observed flux density ratio $(F_{\nu }^{LyC}/F_{\nu }^{UV})_{\rm obs}$ and Lyman alpha equivalent width EW(Lyα), where we confirm the existence of moderately significant correlation among galaxies classified as non-LyC leakers.

scholarly journals Probing star formation and ISM properties using galaxy disk inclination

2018 ◽  
Vol 616 ◽  
pp. A157 ◽  
Author(s):  
S. K. Leslie ◽  
E. Schinnerer ◽  
B. Groves ◽  
M. T. Sargent ◽  
G. Zamorani ◽  
...  
Keyword(s):  
Star Formation ◽  
Radiative Transfer ◽  
Attenuation Correction ◽  
Rest Frame ◽  
Correction Method ◽  
Star Forming ◽  
Local Sample ◽  
Slope Correction ◽  
Galaxy Disk ◽  
Far Ultraviolet

We evaluate dust-corrected far-ultraviolet (FUV) star formation rates (SFRs) for samples of star-forming galaxies at z ~ 0 and z ~ 0.7 and find significant differences between values obtained through corrections based on UV colour, from a hybrid mid-infrared (MIR) plus FUV relation, and from a radiative transfer based attenuation correction method. The performances of the attenuation correction methods are assessed by their ability to remove the dependency of the corrected SFR on inclination, as well as returning, on average, the expected population mean SFR. We find that combining MIR (rest-frame ~ 13 μm) and FUV luminosities gives the most inclination-independent SFRs and reduces the intrinsic SFR scatter of the methods we tested. However, applying the radiative transfer based method also gives corrections to the FUV SFR that are inclination independent and in agreement with the expected SFRs at both z ~ 0 and z ~ 0.7. SFR corrections based on the UV-slope perform worse than the other two methods we tested. For our local sample, the UV-slope method works on average, but does not remove inclination biases. At z ~ 0.7, we find that the UV-slope correction we used locally flattens the inclination dependence compared to the raw FUV measurements, but was not sufficient to correct for the large attenuation observed at z ~ 0.7.

scholarly journals From the far-ultraviolet to the far-infrared – galaxy emission at 0 ≤ z ≤ 10 in the shark semi-analytic model

2019 ◽  
Vol 489 (3) ◽  
pp. 4196-4216 ◽  
Author(s):  
Claudia del P Lagos ◽  
Aaron S G Robotham ◽  
James W Trayford ◽  
Rodrigo Tobar ◽  
Matías Bravo ◽  
...  
Keyword(s):  
Rest Frame ◽  
Spectral Energy Distribution ◽  
Empirical Relation ◽  
Far Infrared ◽  
Initial Mass Function ◽  
Spectral Energy ◽  
Analytic Model ◽  
Star Forming ◽  
Wide Range ◽  
Far Ultraviolet

ABSTRACT We combine the shark semi-analytic model of galaxy formation with the prospect software tool for spectral energy distribution (SED) generation to study the multiwavelength emission of galaxies from the far-ultraviolet (FUV) to the far-infrared (FIR) at 0 ≤ z ≤ 10. We produce a physical model for the attenuation of galaxies across cosmic time by combining a local Universe empirical relation to compute the dust mass of galaxies from their gas metallicity and mass, attenuation curves derived from radiative transfer calculations of galaxies in the eagle hydrodynamic simulation suite, and the properties of shark galaxies. We are able to produce a wide range of galaxies, from the z = 8 star-forming galaxies with almost no extinction, z = 2 submillimetre galaxies, down to the normal star-forming and red-sequence galaxies at z = 0. Quantitatively, we find that shark reproduces the observed (i) z = 0 FUV-to-FIR, (ii) 0 ≤ z ≤ 3 rest-frame K-band, and (iii) 0 ≤ z ≤ 10 rest-frame FUV luminosity functions, (iv) z ≤ 8 UV slopes, (v) the FUV-to-FIR number counts (including the widely disputed 850 μm), (vi) redshift distribution of bright $850\, \mu$m galaxies, and (vii) the integrated cosmic SED from z = 0 to 1 to an unprecedented level. This is achieved without the need to invoke changes in the stellar initial mass function, dust-to-metal mass ratio, or metal enrichment time-scales. Our model predicts star formation in galaxy discs to dominate in the FUV-to-optical, while bulges dominate at the NIR at all redshifts. The FIR sees a strong evolution in which discs dominate at z ≤ 1 and starbursts (triggered by both galaxy mergers and disc instabilities, in an even mix) dominate at higher redshifts, even out to z = 10.

scholarly journals The VIMOS Ultra-Deep Survey: evidence for AGN feedback in galaxies with CIII]-λ1908 Å emission 10.8 to 12.5 Gyr ago

2019 ◽  
Vol 625 ◽  
pp. A51 ◽  
Author(s):  
O. Le Fèvre ◽  
B. C. Lemaux ◽  
K. Nakajima ◽  
D. Schaerer ◽  
M. Talia ◽  
...  
Keyword(s):  
Star Formation ◽  
Rest Frame ◽  
Formation Rate ◽  
Strong Emission ◽  
Star Forming ◽  
Hard Radiation ◽  
Large Dispersion ◽  
Deep Survey ◽  
Complementary Set ◽  
Galaxy Population

We analyze the CIII]-λ1908 Å emission properties in a sample of 3899 star-forming galaxies (SFGs) at 2 <  z <  3.8 drawn from the VIMOS Ultra-Deep Survey (VUDS). We find a median rest-frame equivalent width EW(CIII]) = 2.0 ± 0.2 to 2.2 ± 0.2 Å for the whole SFG population at 2 <  z <  3 and 3 <  z <  4, respectively. About 24% of SFGs are showing EW(CIII]) > 3 Å, including ∼20% with modest emission 3 < EW(CIII]) < 10 Å and ∼4% with strong emission EW(CIII])> 10 Å. A small but significant fraction of 1.2% of SFGs presents strong CIII] emission 20 < EW(CIII]) < 40 Å; the four strongest emitters (EW(CIII]) > 40 Å up to ∼95 Å) are associated with broad-line AGN. While this makes CIII] the second most frequent emission line in the UV rest-frame spectra of SFGs after Lyman-α, this line alone cannot be considered an efficient substitute for measuring a galaxy redshift in the absence of Lyα emission, unless the spectral resolution is R >  3000 to distinguish among different possible doublets. We find a large dispersion in the weak correlation between EW(CIII]) and EW(Lyα), with galaxies showing strong CIII] and no Lyα, and vice versa. The spectra of SFGs with 10 < EW(CIII]) < 40 Å present strong emission lines that include CIV-λ1549, HeII-λ1640, and OIII-λ1664, but also weaker emission features of highly ionized elements such as SiIV-λ1403, NIV-λ1485, NIII-λ1750, or SiIII-λ1888, indicating the presence of a hard radiation field. We present a broad range of observational evidence supporting the presence of AGN in the strong CIII] emitting population. As EW(CIII]) is rising, we identify increasingly powerful outflows with velocities up to 1014 km s−1; this is beyond what stellar winds are commonly producing. The strongest CIII] emitters are preferentially located below the main sequence of star-forming galaxies; the median star formation rate is reduced by a factor of two. In addition, we find that the median stellar age of the strongest emitters is ∼0.8 Gyr, which is about three times that of galaxies with EW(CIII]) < 10 Å. X-ray stacked imaging of the strong CIII] emitters sample show a marginal 2σ detection that is consistent with low-luminosity AGN log(LX(2−10 keV)) ∼ 42.9 erg s−1. Previously presented spectral line analysis and classification support that the strongest emitters require the presence of an AGN. We conclude that this complementary set of evidence is indicative of significant AGN feedback acting in SFGs at 2 <  z <  3.8, and it strongly contributes to star formation quenching. We find that quenching timescales of ∼0.25−0.5 × 109 years are necessary for this AGN feedback to turn part of the star-forming galaxy population with Mstar >  1010 M⊙ at z ∼ 3 into the population of quiescent galaxies observed at redshift z ∼ 1−2.

scholarly journals The time-scales probed by star formation rate indicators for realistic, bursty star formation histories from the FIRE simulations

2020 ◽  
Author(s):  
José A Flores Velázquez ◽  
Alexander B Gurvich ◽  
Claude-André Faucher-Giguére ◽  
James S Bullock ◽  
Tjitske K Starkenburg ◽  
...  
Keyword(s):  
Star Formation ◽  
Time Scales ◽  
Galaxy Formation ◽  
Time Scale ◽  
High Redshift ◽  
Formation Rate ◽  
Star Forming ◽  
Best Fitting ◽  
Far Ultraviolet ◽  
Star Formation Histories

Abstract Understanding the rate at which stars form is central to studies of galaxy formation. Observationally, the star formation rates (SFRs) of galaxies are measured using the luminosity in different frequency bands, often under the assumption of a time-steady SFR in the recent past. We use star formation histories (SFHs) extracted from cosmological simulations of star-forming galaxies from the FIRE project to analyze the time-scales to which the Hα and far-ultraviolet (FUV) continuum SFR indicators are sensitive. In these simulations, the SFRs are highly time variable for all galaxies at high redshift, and continue to be bursty to z = 0 in dwarf galaxies. When FIRE SFHs are partitioned into their bursty and time-steady phases, the best-fitting FUV time-scale fluctuates from its ∼10 Myr value when the SFR is time-steady to ≳100 Myr immediately following particularly extreme bursts of star formation during the bursty phase. On the other hand, the best-fitting averaging time-scale for Hα is generally insensitive to the SFR variability in the FIRE simulations and remains ∼ 5 Myr at all times. These time-scales are shorter than the 100 Myr and 10 Myr time-scales sometimes assumed in the literature for FUV and Hα, respectively, because while the FUV emission persists for stellar populations older than 100 Myr, the time-dependent luminosities are strongly dominated by younger stars. Our results confirm that the ratio of SFRs inferred using Hα vs. FUV can be used to probe the burstiness of star formation in galaxies.

Ubiquitous [O ii] Emission in Quiescent Galaxies at z ≈ 0.85 from the LEGA-C Survey*

2021 ◽  
Vol 923 (1) ◽  
pp. 18
Author(s):  
Michael V. Maseda ◽  
Arjen van der Wel ◽  
Marijn Franx ◽  
Eric F. Bell ◽  
Rachel Bezanson ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Equivalent Width ◽  
Rest Frame ◽  
Galactic Nuclei ◽  
Complete Sample ◽  
Star Forming ◽  
Very Large Telescope ◽  
The Individual ◽  
Stellar Masses ◽  
Early Galaxy

Abstract Using deep rest-frame optical spectroscopy from the Large Early Galaxy Astrophysical Census (LEGA-C) survey, conducted using VIMOS on the ESO Very Large Telescope, we search for low-ionization [O ii] λ λ 3726,3729 emission in the spectra of a mass-complete sample of z ≈ 0.85 galaxies. We find that 59% of UVJ-quiescent (i.e., non-star-forming) galaxies in the sample have [O ii] emission detected above our completeness limit of 1.5 Å, and the median-stacked spectrum of the remaining sample also shows [O ii] emission. The overall fraction of sources with [O ii] above our equivalent width limit is comparable to what we find in the low-redshift universe from GAMA and MASSIVE, except perhaps at the highest stellar masses (>1011.5 M ⊙). However, stacked spectra for the individual low-equivalent-width systems uniquely indicates ubiquitous [O ii] emission in the higher-z LEGA-C sample, with typical [O ii] luminosities per unit stellar mass that are a factor of ×3 larger than the lower-z GAMA sample. Star formation at higher-z could play a role in producing the [O ii] emission, although it is unlikely to provide the bulk of the ionizing photons. More work is required to fully quantify the contributions of evolved stellar populations or active galactic nuclei to the observed spectra.

scholarly journals MUSE observations towards the lensing cluster A2744: Intersection between the LBG and LAE populations at z ∼ 3–7

2020 ◽  
Vol 644 ◽  
pp. A39
Author(s):  
G. de La Vieuville ◽  
R. Pelló ◽  
J. Richard ◽  
G. Mahler ◽  
L. Lévêque ◽  
...  
Keyword(s):  
Total Population ◽  
Relative Distribution ◽  
Star Forming ◽  
Lyman Alpha ◽  
Alpha Emitters ◽  
Lyman Break Galaxies ◽  
Opposite Trend ◽  
Three Samples ◽  
Lyman Alpha Emitters ◽  
Two Populations

We present a study of the intersection between the populations of star forming galaxies selected as either Lyman break galaxies (LBGs) or Lyman-alpha emitters (LAEs) in the redshift range 2.9 − 6.7 and within the same volume of universe sampled by the Multi-Unit Spectroscopic Explorer (MUSE) behind the Hubble Frontier Fields lensing cluster A2744. We define three samples of star-forming galaxies: LBG galaxies with an LAE counterpart (92 galaxies), LBG galaxies without an LAE counterpart (408 galaxies), and LAE galaxies without an LBG counterpart (46 galaxies). All these galaxies are intrinsically faint because of the lensing nature of the sample (M1500 ≥ −20.5). The fraction of LAEs among all selected star-forming galaxies increases with redshift up to z ∼ 6 and decreases for higher redshifts, in agreement with previous findings. The evolution of LAE/LBG populations with UV magnitude and Lyα luminosity shows that the LAE selection is able to identify intrinsically UV faint galaxies with M1500 ≥ −15 that are typically missed in the deepest lensing photometric surveys. The LBG population seems to fairly represent the total population of star-forming galaxies down to M1500 ∼ −15. Galaxies with M1500 < −17 tend to have SFRLyα < SFRuv, whereas the opposite trend is observed within our sample for faint galaxies with M1500 > −17, including galaxies only detected by their Lyα emission, with a large scatter. These trends, previously observed in other samples of star-forming galaxies at high-z, are seen here for very faint M1500 ∼ −15 galaxies; that is, much fainter than in previous studies. The present results show no clear evidence for an intrinsic difference between the properties of the two populations selected as LBG and/or LAE. The observed trends could be explained by a combination of several phenomena, like the existence of different star-formation regimes, the dust content, the relative distribution and morphology of dust and stars, or the stellar populations.

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