scholarly journals Intense C III] λλ1907,1909 emission from a strong Lyman continuum emitting galaxy

2018 ◽  
Vol 616 ◽  
pp. L14 ◽  
Author(s):  
D. Schaerer ◽  
Y. I. Izotov ◽  
K. Nakajima ◽  
G. Worseck ◽  
J. Chisholm ◽  
...  
Keyword(s):  
Equivalent Width ◽  
Production Efficiency ◽  
Rest Frame ◽  
Stellar Population ◽  
Uv Spectrum ◽  
Star Forming ◽  
Uv Emission ◽  
Lyman Continuum ◽  
Low Metallicity ◽  
Imaging Spectrograph

We have obtained the first complete ultraviolet (UV) spectrum of a strong Lyman continuum (LyC) emitter at low redshift – the compact, low-metallicity, star-forming galaxy J1154+2443 – with a Lyman continuum escape fraction of 46% discovered recently. The Space Telescope Imaging Spectrograph spectrum shows strong Lyα and C III] λ1909 emission, as well as O III] λ1666. Our observations show that strong LyC emitters can have UV emission lines with a high equivalent width (e.g. EW(C III]) = 11.7 ± 2.9 Å rest-frame), although their equivalent widths should be reduced due to the loss of ionizing photons. The intrinsic ionizing photon production efficiency of J1154+2443 is high, log(ξ0ion = 25.56 erg−1 Hz), comparable to that of other recently discovered z ~ 0.3−0.4 LyC emitters. Combining our measurements and earlier determinations from the literature, we find a trend of increasing ξ0ion with increasing C III] λ1909 equivalent width, which can be understood by a combination of decreasing stellar population age and metallicity. Simple ionization and density-bounded photoionization models can explain the main observational features including the UV spectrum of J1154+2443.

scholarly journals The mean Hα EW and Lyman-continuum photon production efficiency for faint z ≈ 4−5 galaxies

2019 ◽  
Vol 627 ◽  
pp. A164 ◽  
Author(s):  
Daniel Lam ◽  
Rychard J. Bouwens ◽  
Ivo Labbé ◽  
Joop Schaye ◽  
Kasper B. Schmidt ◽  
...  
Keyword(s):  
Production Rate ◽  
Production Efficiency ◽  
Rest Frame ◽  
Strong Dependence ◽  
Photon Production ◽  
Star Forming ◽  
Lyman Continuum ◽  
The Mean

We present the first measurements of the Lyman-continuum photon production efficiency ξion, 0 at z ∼ 4–5 for galaxies fainter than 0.2 L* (−19 mag). ξion, 0 quantifies the production rate of ionizing photons with respect to the UV luminosity density assuming a fiducial escape fraction of zero. Extending previous measurements of ξion, 0 to the faint population is important, as ultra-faint galaxies are expected to contribute the bulk of the ionizing emissivity. We probe ξion, 0 to such faint magnitudes by taking advantage of 200-h depth Spitzer/IRAC observations from the GREATS program and ≈300 3 <  z <  6 galaxies with spectroscopic redshifts from the MUSE GTO Deep + Wide programs. Stacked IRAC [3.6]−[4.5] colors are derived and used to infer the Hα rest-frame equivalent widths, which range from 403 Å to 2818 Å. The derived ξion, 0 is log10(ξion,0/Hz erg−1) = 25.36 ± 0.08 over −20.5 <  MUV <  −17.5, similar to those derived for brighter galaxy samples at the same redshift and therefore suggesting that ξion shows no strong dependence on MUV. The ξion, 0 values found in our sample imply that the Lyman-continuum escape fraction for MUV ≈ −19 star-forming galaxies cannot exceed ≈8–20% in the reionization era.

scholarly journals The SFR Efficiency of HI Gas in the Outskirts of Star Forming Galaxies

2016 ◽  
Vol 11 (S321) ◽  
pp. 360-362
Author(s):  
Marc Rafelski
Keyword(s):  
Star Formation ◽  
Atomic Hydrogen ◽  
Rest Frame ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Hydrogen Gas ◽  
Star Forming ◽  
Uv Emission ◽  
Atomic Gas

AbstractIn order to understand the origin of the decreased star formation rate (SFR) efficiency of neutral atomic hydrogen gas measured in Damped Lyα Systems (DLAs) at z ~ 3, we measure the SFR efficiency of atomic gas at z ~ 1, z ~ 2, and z ~ 3 around star-forming galaxies. We create galaxy stacks in these three redshift bins, and measure the SFR efficiency by combining DLA absorber statistics with the observed rest-frame UV emission in the galaxies’ outskirts. We find that the SFR efficiency of Hi gas is ~ 3% of that predicted by the KS relation. We find no significant evolution in the SFR efficiency with redshift, although simulations and models predict a decreasing SFR efficiency with decreasing metallicity and thus with increasing redshift. We discuss possible explanations for this decreased efficiency without an evolution with redshift.

scholarly journals The properties of He IIλ1640 emitters at z ∼  2.5–5 from the VANDELS survey

2020 ◽  
Vol 636 ◽  
pp. A47 ◽  
Author(s):  
A. Saxena ◽  
L. Pentericci ◽  
M. Mirabelli ◽  
D. Schaerer ◽  
R. Schneider ◽  
...  
Keyword(s):  
Star Formation ◽  
Rest Frame ◽  
Stellar Population ◽  
Stellar Ages ◽  
Significant Difference ◽  
Consistent Manner ◽  
Multi Wavelength ◽  
Low Metallicity ◽  
Stellar Masses ◽  
X Ray Binaries

Aims. Strong He II emission is produced by low-metallicity stellar populations. Here, we aim to identify and study a sample of He IIλ1640-emitting galaxies at redshifts of z ∼ 2.5 − 5 in the deep VANDELS spectroscopic survey. Methods. We identified a total of 33 Bright He II emitters (S/N >  2.5) and 17 Faint emitters (S/N <  2.5) in the VANDELS survey and used the available deep multi-wavelength data to study their physical properties. After identifying seven potential AGNs in our sample and discarding them from further analysis, we divided the sample of Bright emitters into 20 Narrow (FWHM <  1000 km s−1) and 6 Broad (FWHM >  1000 km s−1) He II emitters. We created stacks of Faint, Narrow, and Broad emitters and measured other rest-frame UV lines such as O III] and C III] in both individual galaxies and stacks. We then compared the UV line ratios with the output of stellar population-synthesis models to study the ionising properties of He II emitters. Results. We do not see a significant difference between the stellar masses, star-formation rates, and rest-frame UV magnitudes of galaxies with He II and no He II emission. The stellar population models reproduce the observed UV line ratios from metals in a consistent manner, however they under-predict the total number of He II ionising photons, confirming earlier studies and suggesting that additional mechanisms capable of producing He II are needed, such as X-ray binaries or stripped stars. The models favour subsolar metallicities (∼0.1 Z⊙) and young stellar ages (106 − 107 years) for the He II emitters. However, the metallicity measured for He II emitters is comparable to that of non-He II emitters at similar redshifts. We argue that galaxies with He II emission may have undergone a recent star-formation event, or may be powered by additional sources of He II ionisation.

scholarly journals The [O iii]+H β equivalent width distribution at z ≃ 7: implications for the contribution of galaxies to reionization

2020 ◽  
Vol 500 (4) ◽  
pp. 5229-5248
Author(s):  
Ryan Endsley ◽  
Daniel P Stark ◽  
Jacopo Chevallard ◽  
Stéphane Charlot
Keyword(s):  
Star Formation ◽  
Standard Deviation ◽  
Equivalent Width ◽  
Production Efficiency ◽  
Massive Star ◽  
Star Clusters ◽  
Strong Variation ◽  
Star Forming ◽  
Width Distribution ◽  
Intense Star Formation

ABSTRACT We quantify the distribution of [O iii]+H β line strengths at z ≃ 7 using a sample of 20 bright ($\mathrm{M}_{\mathrm{UV}}^{}$ ≲ –21) galaxies. We select these systems over wide-area fields (2.3 deg2 total) using a new colour-selection that precisely selects galaxies at z ≃ 6.63–6.83, a redshift range where blue Spitzer/IRAC [3.6]−[4.5] colours unambiguously indicate strong [O iii]+H β emission. These 20 galaxies suggest a lognormal [O iii]+H β EW distribution with median EW = 759$^{+112}_{-113}$ Å and standard deviation = 0.26$^{+0.06}_{-0.05}$ dex. We find no evidence for strong variation in this EW distribution with UV luminosity. The typical [O iii]+H β EW at z ≃ 7 implied by our sample is considerably larger than that in massive star-forming galaxies at z ≃ 2, consistent with a shift towards larger average sSFR (4.4 Gyr−1) and lower metallicities (0.16 Z⊙). We also find evidence for the emergence of a population with yet more extreme nebular emission ([O iii]+H β EW &gt; 1200 Å) that is rarely seen at lower redshifts. These objects have extremely large sSFR (&gt;30 Gyr−1), as would be expected for systems undergoing a burst or upturn in star formation. While this may be a short-lived phase, our results suggest that 20 per cent of the z ≃ 7 population has such extreme nebular emission, implying that galaxies likely undergo intense star formation episodes regularly at z &gt; 6. We argue that this population may be among the most effective ionizing agents in the reionization era, both in terms of photon production efficiency and escape fraction. We furthermore suggest that galaxies passing through this large sSFR phase are likely to be very efficient in forming bound star clusters.

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.

scholarly journals Stellar populations of galaxies in the ALHAMBRA survey up to z ∼ 1

2019 ◽  
Vol 631 ◽  
pp. A156 ◽  
Author(s):  
L. A. Díaz-García ◽  
A. J. Cenarro ◽  
C. López-Sanjuan ◽  
I. Ferreras ◽  
M. Cerviño ◽  
...  
Keyword(s):  
Star Formation ◽  
Rest Frame ◽  
Stellar Population ◽  
Spectral Energy Distribution ◽  
Formation Rate ◽  
Stellar Mass ◽  
Spectral Energy ◽  
Population Parameters ◽  
Star Forming ◽  
Set Constraints

Aims. Our aim is to determine the distribution of stellar population parameters (extinction, age, metallicity, and star formation rates) of quiescent galaxies within the rest-frame stellar mass–colour diagrams and UVJ colour–colour diagrams corrected for extinction up to z ∼ 1. These novel diagrams reduce the contamination in samples of quiescent galaxies owing to dust-reddened galaxies, and they provide useful constraints on stellar population parameters only using rest-frame colours and/or stellar mass. Methods. We set constraints on the stellar population parameters of quiescent galaxies combining the ALHAMBRA multi-filter photo-spectra with our fitting code for spectral energy distribution, MUlti-Filter FITting (MUFFIT), making use of composite stellar population models based on two independent sets of simple stellar population (SSP) models. The extinction obtained by MUFFIT allowed us to remove dusty star-forming (DSF) galaxies from the sample of red UVJ galaxies. The distributions of stellar population parameters across these rest-frame diagrams are revealed after the dust correction and are fitted by LOESS, a bi-dimensional and locally weighted regression method, to reduce uncertainty effects. Results. Quiescent galaxy samples defined via classical UVJ diagrams are typically contaminated by a ∼20% fraction of DSF galaxies. A significant part of the galaxies in the green valley are actually obscured star-forming galaxies (∼30–65%). Consequently, the transition of galaxies from the blue cloud to the red sequence, and hence the related mechanisms for quenching, seems to be much more efficient and faster than previously reported. The rest-frame stellar mass–colour and UVJ colour–colour diagrams are useful for constraining the age, metallicity, extinction, and star formation rate of quiescent galaxies by only their redshift, rest-frame colours, and/or stellar mass. Dust correction plays an important role in understanding how quiescent galaxies are distributed in these diagrams and is key to performing a pure selection of quiescent galaxies via intrinsic colours.

scholarly journals A young star-forming galaxy at z = 3.5 with an extended Lyman α halo seen with MUSE

2015 ◽  
Vol 11 (A29B) ◽  
pp. 820-821
Author(s):  
Vera Patrício ◽  
Johan Richard ◽  
Anne Verhamme ◽  
Keyword(s):  
Physical Properties ◽  
Gas Phase ◽  
Surface Brightness ◽  
Spatial Information ◽  
Young Star ◽  
Star Forming ◽  
Uv Emission ◽  
Low Metallicity ◽  
Reasonable Description ◽  
First Time

AbstractWe present MUSE observations of a typical (M⋆ = 6 × 109M⊙) young lensed galaxy at z=3.5, for which we obtain 2D resolved spatial information of Ly α and, for the first time, of C iii] emission. We also derive important physical properties from several UV emission and absorption lines, rarely seen at these redshifts. Stellar and gas-phase metallicities point towards a low metallicity object. We model the Ly α line and surface brightness profile using a radiative transfer code in an expanding gas shell, finding that this model provides a reasonable description of both observables.

scholarly journals Is the Bremer Deep Field reionized, at z ∼ 7?

2021 ◽  
Vol 503 (3) ◽  
pp. 4242-4249
Author(s):  
J M Rodríguez Espinosa ◽  
J M Mas-Hesse ◽  
R Calvi
Keyword(s):  
Production Efficiency ◽  
Intergalactic Medium ◽  
Evolutionary Model ◽  
Photon Production ◽  
Analytic Model ◽  
Star Forming ◽  
Lyman Continuum ◽  
The Universe

ABSTRACT We show herein that the population of star-forming galaxies in the Bremer Deep Field (BDF) has enough ionizing power to form two large ionized bubbles that could be in the process of merging into a large one with a volume of 14 000 cMpc3. The sources identified in the BDF have been completed with a set of expected low-luminosity sources at z ∼ 7. We have estimated the number of ionizing photons per second produced by the different star-forming galaxies in the BDF. This number has been compared with the number that would be required to ionize the bubbles around the two overdense regions. We have used, as reference, ionizing emissivities derived from the AMIGA (Analytic Model of Intergalactic-medium and Galaxies) cosmological evolutionary model. We find that even using the most conservative estimates, with a Lyman continuum escape fraction of 10${{\ \rm per\ cent}}$, the two regions we have defined within the BDF would be reionized. Assuming more realistic estimates of the ionizing photon production efficiency, both bubbles would be in the process of merging into a large reionized bubble, such as those that through percolation completed the reionization of the Universe by z = 6. The rather small values of the escape fraction required to reionize the BDF are compatible with the low fraction of faint Ly α emitters identified in the BDF. Finally, we confirm that the low-luminosity sources represent indeed the main contributors to the BDF ionizing photon production.

scholarly journals Rest-frame UV spectroscopy of extreme [OIII] emitters at 1.3 < z < 3.7: Toward a high-redshift UV reference sample for JWST

2020 ◽  
Author(s):  
Mengtao Tang ◽  
Daniel P Stark ◽  
Jacopo Chevallard ◽  
Stéphane Charlot ◽  
Ryan Endsley ◽  
...  
Keyword(s):  
Rest Frame ◽  
Uv Spectroscopy ◽  
High Redshift ◽  
Reference Sample ◽  
Line Emission ◽  
Uv Emission ◽  
Consistent Picture ◽  
Low Metallicity ◽  
Extreme Sensitivity ◽  
Galaxy Population

Abstract Deep spectroscopy of galaxies in the reionization era has revealed intense C III] and C IV line emission (EW &gt;15 − 20 Å). In order to interpret the nebular emission emerging at z &gt; 6, we have begun targeting rest-frame UV emission lines in galaxies with large specific star formation rates (sSFRs) at 1.3 &lt; z &lt; 3.7. We find that C III] reaches the EWs seen at z &gt; 6 only in large sSFR galaxies with [O III]+Hβ EW &gt;1500 Å. In contrast to previous studies, we find that many galaxies with intense [O III] have weak C III] emission (EW =5 − 8 Å), suggesting that the radiation field associated with young stellar populations is not sufficient to power strong C III]. Photoionization models demonstrate that the spread in C III] among systems with large sSFRs ([O III]+Hβ EW &gt;1500 Å) is driven by variations in metallicity, a result of the extreme sensitivity of C III] to electron temperature. We find that the strong C III] emission seen at z &gt; 6 (EW &gt;15 Å) requires metal poor gas (≃ 0.1 Z⊙) whereas the weaker C III] emission in our sample tends to be found at moderate metallicities (≃ 0.3 Z⊙). The luminosity distribution of the C III] emitters in our z ≃ 1 − 3 sample presents a consistent picture, with stronger emission generally linked to low luminosity systems (MUV &gt; −19.5) where low metallicities are more likely. We quantify the fraction of strong C III] and C IV emitters at z ≃ 1 − 3, providing a baseline for comparison against z &gt; 6 samples. We suggest that the first UV line detections at z &gt; 6 can be explained if a significant fraction of the early galaxy population is found at large sSFR (&gt;200 Gyr−1) and low metallicity (&lt;0.1 Z⊙).

Active and dust obscured star-forming galaxies at z ∼ 4 probed with UV spectral slope beta

2019 ◽  
Vol 15 (S341) ◽  
pp. 323-325
Author(s):  
Satoshi Yamanaka ◽  
Toru Yamada
Keyword(s):  
Star Formation ◽  
Rest Frame ◽  
Stellar Population ◽  
Significant Fraction ◽  
Spectral Slope ◽  
Ultraviolet Continuum ◽  
Active Star ◽  
Star Forming ◽  
Lyman Break Galaxies ◽  
Deep Survey

AbstractWe investigate the stellar population of star-forming galaxies at z ∼ 4 by focusing on their slope of rest-frame ultraviolet continuum called UV spectral slope β. We analyze the sample of bright Lyman Break Galaxies (LBGs) with Subaru/i′≤26.0in the Subaru/XMM-Newton Deep Survey field. Our detailed SED fitting analysis indicates that the LBGs with observed UV slope > −1.7, , Av > 1.0, and intrinsic UV slope < −2.5 are the intrinsically active star-forming galaxies with star formation rates larger than a few × 102 M⊙yr−1. A significant fraction of the UV-selected LBGs at z ∼ 4 is on-going active and dust obscured star-forming galaxies.

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