J/ApJ/938/16 Characterizing extreme em. line gal. II. COS & LBT (Olivier+, 2022)
Characterizing extreme emission line galaxies.
II. A self-consistent model of their ionizing spectrum.
Olivier G.M., Berg D.A., Chisholm J., Erb D.K., Pogge R.W., Skillman E.D.
<Astrophys. J., 938, 16 (2022)>
=2022ApJ...938...16O 2022ApJ...938...16O
ADC_Keywords: Galaxies, spectra; Redshifts; Equivalent widths;
Spectra, ultraviolet; Optical
Keywords: Dwarf galaxies ; Ultraviolet astronomy ; Galaxy chemical evolution ;
Galaxy spectroscopy ; High-redshift galaxies ; Emission line galaxies
Abstract:
Observations of high-redshift galaxies (z>5) have shown that these
galaxies have extreme emission lines with equivalent widths much
larger than their local star-forming counterparts. Extreme emission
line galaxies (EELGs) in the nearby universe are likely analogs to
galaxies during the Epoch of Reionization and provide nearby
laboratories to understand the physical processes important to the
early universe. We use Hubble Space Telescope/Cosmic Origins
Spectrograph and Large Binocular Telescope/Multi-Object Double
Spectrographs spectra to study two nearby EELGs, J104457 and J141851.
The far-UV spectra indicate that these two galaxies contain stellar
populations with ages ≲10Myr and metallicities ≤0.15Z☉. We use
photoionization modeling to compare emission lines from models of
single-age bursts of star formation to observed emission lines and
find that the single-age bursts do not reproduce high-ionization lines
including [OIII] or very-high-ionization lines like HeII or OIV].
Photoionization modeling using the stellar populations fit from the UV
continuum similarly is not capable of reproducing the very-high-energy
emission lines. We add a blackbody to the stellar populations fit from
the UV continuum to model the necessary high-energy photons to
reproduce the very-high-ionization lines of HeII and OIV]. We find
that we need a blackbody of 80000K and ∼45%-55% of the luminosity from
the blackbody and young stellar population to reproduce the
very-high-ionization lines while simultaneously reproducing the low-,
intermediate-, and high-ionization emission lines. Our self-consistent
model of the ionizing spectra of two nearby EELGs indicates the
presence of a previously unaccounted-for source of hard ionizing
photons in reionization analogs.
Description:
In this work we used far-UV (FUV) spectra taken with the Cosmic
Origins Spectrograph (COS) on the HST that were first reported in
Berg+ (2016ApJ...827..126B 2016ApJ...827..126B and 2019ApJ...874...93B 2019ApJ...874...93B) and
Berg+ (2019ApJ...878L...3B 2019ApJ...878L...3B) from the HST Project ID 15465.
See Section 2.1.
Recently, Paper I (Berg+ 2021ApJ...922..170B 2021ApJ...922..170B) presented a more
detailed examination of the extreme emission lines in J104457 and
J141851 and their chemical abundances, using the HST/COS G160M spectra
together with new optical spectra from the Multi-Object Double
Spectrographs (MODS) on the Large Binocular Telescope (LBT).
MODS optical spectra of J104457 and J141851 were obtained on the UT
dates of 2018 May 19 and 18, respectively. We obtained simultaneous,
moderate-resolution blue (R∼1850) and red (R∼2300) spectra.
See Section 2.2.
Objects:
---------------------------------------------------------------
RA (ICRS) DE Designation(s)
---------------------------------------------------------------
10 44 57.79 +03 53 13.1 J104457 = SDSS J104457.79+035313.1
14 18 51.12 +21 02 39.9 J141851 = SDSS J141851.12+210239.7
---------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 135 2 Extreme UV emission-line galaxy properties
sp/* . 2 Individual Optical LBT/MODS spectra of J104457
and J141851 in ASCII format (Data behind Figure 2)
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See also:
J/A+AS/103/97 : Grids of stellar models V. (Meynet+ 1994)
J/A+AS/125/229 : A standard stellar library (Lejeune+ 1997)
J/ApJS/161/240 : High-ionization em. in metal-deficient BCDs (Thuan+, 2005)
J/ApJ/636/214 : HII regions in dwarf irregular galaxies (van Zee+, 2006)
J/ApJ/742/111 : Extreme emission-line galaxies in CANDELS (van der Wel+, 2011)
J/ApJ/795/165 : Line ratios in z∼2-3 gal. from KBSS-MOSFIRE (Steidel+, 2014)
J/ApJ/806/16 : CHemical Abund. of Spirals (CHAOS). I. NGC628 (Berg+, 2015)
J/ApJ/803/34 : z∼4-10 galaxies from HST legacy fields (Bouwens+, 2015)
J/ApJ/810/71 : UV mag of candidate galaxies at 3~<z~<8.5 (Finkelstein+, 2015)
J/ApJ/813/82 : z<0.06 broad-line AGN emission-line measures (Reines+, 2015)
J/ApJ/814/L6 : CIII] emission in near & far star-forming gal. (Rigby+, 2015)
J/ApJ/835/113 : Gal. ≳6 from the Hubble Frontier Fields (Livermore+, 2017)
J/AJ/155/104 : MEGaSaURA. I. The sample and the spectra (Rigby+, 2018)
J/ApJ/853/87 : MEGaSaURA. II. Stacked spectra (Rigby+, 2018)
J/A+A/629/A134 : Radiative contribution from stripped stars (Goetberg+, 2019)
J/ApJ/888/36 : SDSS/FIRST dwarf gal. with VLA high res. obs. (Reines+, 2020)
J/ApJ/921/91 : Catastrophic cooling in superwinds. II. (Danehkar+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- ID Galaxy identifier (JHHMMSS)
9- 12 A4 --- Ref Reference (1)
14- 15 I2 h RAh Hour of right ascension (J2000)
17- 18 I2 min RAm Minute of right ascension (J2000)
20- 24 F5.2 s RAs Second of right ascension (J2000)
26 A1 --- DE- Sign of declination (J2000)
27- 28 I2 deg DEd Degree of declination (J2000)
30- 31 I2 arcmin DEm Arcminute of declination (J2000)
33- 37 F5.2 arcsec DEs Arcsecond of declination (J2000)
39- 43 F5.3 --- z [0.009/0.013] Redshift
45- 48 F4.2 [Msun] logMass [6.6/6.8] Log of total stellar mass
50- 54 F5.2 [Msun/yr] logSFR [-1.2/-0.8] Log of stellar formation
rate
56- 60 F5.2 [yr-1] logsSFR [-7.8/-7.6] Log of specific stellar
formation rate
62- 66 F5.3 mag E(B-V) [0.07/0.14] Reddening E (B-V)
68- 71 F4.2 --- Z Metallicity, 12+log (O/H)
73- 77 F5.3 --- e_Z Z uncertainty
79- 83 F5.2 --- logU [-2.42/-1.7] Ionization parameter
85- 89 F5.2 0.1nm EWOIII1661 OIII]λ1661 equivalent width
91- 95 F5.2 0.1nm EWOIII1666 OIII]λ1666 equivalent width
97- 101 F5.2 0.1nm EWCIV1548 CIVλ1548 equivalent width
103- 107 F5.2 0.1nm EWCIV1550 CIVλ1550 equivalent width
109- 113 F5.2 0.1nm EWHeII [-2.82/-2.75] HeIIλ1640
equivalent width
115- 118 F4.1 km/s DelVOIII [64.7/87.3] Velocity width (FWHM),
ΔV, of OIII]λ1666
120- 124 F5.1 km/s DelVCIVb Velocity width (FWHM), ΔV, of
CIVλ1548 blue
126- 129 F4.1 km/s DelVCICr Velocity width (FWHM), ΔV, of
CIVλ1548 red
131- 135 F5.1 km/s FWHM [103.5/188.4] Spectral resolution from
COS used in our continuum fitting
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Note (1): Reference as follows:
B16 = Berg et al. 2016ApJ...827..126B 2016ApJ...827..126B
B19b = Berg et al. 2019ApJ...878L...3B 2019ApJ...878L...3B
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
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1- 7 F7.2 0.1nm lambda [3100/9900] Wavelength, Angstroms
9- 20 E12.5 cW/m2/nm Flux [-1.4e-17/1.2e-14] Flux, erg/s/cm2/Å
22- 32 E11.5 cW/m2/nm e_Flux [6.3e-18/9.2e-17] Uncertainty in Flux
34- 44 E11.5 cW/m2/nm Sky [1.1e-18/2.2e-17] Sky flux contribution,
erg/s/cm2/Å
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History:
From electronic version of the journal
References:
Berg et al. Paper I. 2021ApJ...922..170B 2021ApJ...922..170B
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 12-Aug-2024