J/A+A/686/A185 UV bright star-forming galaxies spectra (Upadhyaya+, 2024)
Evidence for very massive stars in extremely UV bright star-forming galaxies
at z ∼ 2.2 - 3.6.
Upadhyaya A., Marques-Chaves R., Schaerer D., Martins F., Perez-Fournon I.,
Palacios A., Stanway E.R.
<Astron. Astrophys. 686, A185 (2024)>
=2024A&A...686A.185U 2024A&A...686A.185U (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies ; Ultraviolet ; Spectra, ultraviolet
Keywords: stars: massive - galaxies: high-redshift - galaxies: starburst -
ultraviolet: galaxies
Abstract:
We present a comprehensive analysis of the presence of very massive
stars (VMS>100M☉) in the integrated spectra of 13 UVbright
star-forming galaxies at 2.2≲z≲3.6 taken with the Gran Telescopio
Canarias (GTC). These galaxies have very high UV absolute magnitudes
(MUV~-24), intense star formation (star formation rate
∼100-1000M_☉/yr), and metallicities in the range of
12+log(O/H)∼8.10-8.50 inferred from strong rest-optical lines. The GTC
rest-UV spectra reveal spectral features indicative of very young
stellar populations with VMS, such as strong P-Cygni line profiles in
the wind lines NV λ1240 and CIV λ1550 along with intense
and broad He ii 1640 emission with equivalent width
(EW0)∼1.40-4.60Å, and full width half maximum
(FWHM)∼1150-3170km/s. A Comparison with known VMS-dominated sources
and typical galaxies without VMS reveals that some UV-bright galaxies
closely resemble VMS-dominated clusters (e.g., R136 cluster). The
presence of VMS is further supported by a quantitative comparison of
the observed strength of the He ii emission with population synthesis
models with and without VMS, where models with VMS are clearly
preferred. Employing an empirical threshold for EW0 (HeII)≥3.0Å,
along with the detection of other VMS-related spectral profiles (NIV
λ1486; λ1719), we classify nine out of 13 UV-bright
galaxies as VMS-dominated sources. This high incidence of
VMS-dominated sources in the UV-bright galaxy population (∼70%)
contrasts significantly with the negligible presence of VMS in typical
L*UV LBGs at similar redshifts (<1%). Our results thus indicate that
VMS are common in UV-bright galaxies, suggesting a different initial
mass function (IMF) with upper mass limits between 175M☉ and
475M☉.
Description:
Spectra of 13 sources and their stack are provided.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 95 13 Summary of the GTC observations
stack.dat 30 1420 Stack spectrum of UV-bright galaxies
sp/* . 13 Individual spectra
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Name (JHHMM+DDMM)
11 A1 --- n_Name [abc] Note on Name (1)
13- 14 I2 h RAh Right ascension (J2000)
16- 17 I2 min RAm Right ascension (J2000)
19- 23 F5.2 s RAs Right ascension (J2000)
25 A1 --- DE- Declination sign (J2000)
26- 27 I2 deg DEd Declination (J2000)
29- 30 I2 arcmin DEm Declination (J2000)
32- 36 F5.2 arcsec DEs Declination (J2000)
38- 42 F5.3 --- z Redshift
44- 48 F5.2 mag Rmag R-band magnitude (AB)
50- 59 A10 "date" DateO Optical spectroscopy observation date
61- 64 I4 s ExpTimeO Optical spectroscopy exposure time
66- 75 A10 "date" DateN Near-IR spectroscopy observation date
77- 80 I4 s ExpTimeN ? Near-IR spectroscopy exposure time
82- 95 A14 --- FileName Name of the spectrum file in subdirectory sp
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Note (1): Data already presented in the following papers:
a = Marques-Chaves et al. (2021MNRAS.507..524M 2021MNRAS.507..524M)
b = Marques-Chaves et al. (2020MNRAS.499L.105M 2020MNRAS.499L.105M)
c = Marques-Chaves et al. (2022MNRAS.517.2972M 2022MNRAS.517.2972M)
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Byte-by-byte Description of file: stack.dat
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Bytes Format Units Label Explanations
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1- 4 I4 0.1nm lambda Rest-frame wavelength
7- 18 E12.6 --- Flux Flux in Flambda unit
20- 30 E11.6 --- e_Flux 1 sigma uncertainty associated with the
flux in Flambda unit
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 F7.2 0.1nm lambda Observed wavelength
10- 21 E12.6 --- Flux Flux in Flambda unit
24- 36 E13.6 --- e_Flux [] 1 sigma uncertainty associated with the
flux in Flambda unit (1)
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Note (1): Negative values when Flux=0.
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Acknowledgements:
Ankur Upadhyaya, ankur.upadhyaya(at)warwick.ac.uk
(End) Patricia Vannier [CDS] 05-Apr-2024