J/ApJ/930/135 Chandra obs. of low-metallicity star-forming gal. (Lehmer+, 2022)
Elevated hot gas and high-mass X-ray binary emission in low-metallicity
galaxies: implications for nebular ionization and intergalactic medium heating
in the early universe.
Lehmer B.D., Eufrasio R.T., Basu-Zych A., Garofali K., Gilbertson W.,
Mesinger A., Yukita M.
<Astrophys. J., 930, 135 (2022)>
=2022ApJ...930..135L 2022ApJ...930..135L
ADC_Keywords: Galaxies, optical; X-ray sources; Energy distributions;
Intergalactic medium
Keywords: High mass x-ray binary stars ; Metallicity ; Star formation ;
Starburst galaxies ; X-ray binary stars ; X-ray astronomy ;
Compact objects
Abstract:
High-energy emission associated with star formation has been proposed
as a significant source of interstellar medium (ISM) ionization in
low-metallicity starbursts and an important contributor to the heating
of the intergalactic medium (IGM) in the high-redshift (z≳8)
universe. Using Chandra observations of a sample of 30 galaxies at
D∼200-450Mpc that have high specific star formation rates of
3-9Gyr-1 and metallicities near Z∼0.3Z☉, we provide new
measurements of the average 0.5-8keV spectral shape and normalization
per unit star formation rate (SFR). We model the sample-combined X-ray
spectrum as a combination of hot gas and high-mass X-ray binary (HMXB)
populations and constrain their relative contributions. We derive
scaling relations of logL0.5-8keVHMXB/SFR=40.19±0.06 and
logL0.5-2keVgas/SFR=39.58-0.28+0.17; significantly elevated
compared to local relations. The HMXB scaling is also somewhat higher
than L0.5-8keVHMXB-SFR-Z relations presented in the literature,
potentially due to our galaxies having relatively low HMXB obscuration
and young and X-ray luminous stellar populations. The elevation of the
hot gas scaling relation is at the level expected for diminished
attenuation due to a reduction of metals; however, we cannot conclude
that an L0.5-2keVgas-SFR-Z relation is driven solely by changes in
ISM metal content. Finally, we present SFR-scaled spectral models
(both emergent and intrinsic) that span the X-ray-to-IR band,
providing new benchmarks for studies of the impact of ISM ionization
and IGM heating in the early universe.
Description:
We started by using the starlight-subtracted emission-line fluxes
published in the SDSS DR7 MPA-JHU value-added catalogs to identify
potential AGN and calculate metallicities for a sample of galaxies
that had Hα, Hβ, OIII, and NII emission-line fluxes
detected at the >3σ level. After the selection process described
in Section 2, we observed a sample of 30 galaxies with Chandra through
the combination of archival observations for three galaxies
(J002101.0+005248.1, J080619.5+194927.3, and J225140.3+132713.4; see
Basu-Zych+ 2013ApJ...774..152B 2013ApJ...774..152B) and new observations of the remaining
27 objects (PI: Lehmer).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 103 30 Galaxy sample properties
table2.dat 118 30 X-ray properties of sample
table4.dat 59 100 SFR-normalized model SED
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
II/349 : The Pan-STARRS release 1 (PS1) Survey - DR1 (Chambers+, 2016)
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
J/ApJ/681/1163 : Late-type galaxies in Chandra deep fields (Lehmer+, 2008)
J/MNRAS/419/2095 : HMXBs in nearby galaxies (Mineo+, 2012)
J/MNRAS/421/1043 : Emission-line galaxies from SDSS DR7 (Shirazi+, 2012)
J/ApJ/776/L31 : Energy feedback from XRB from z=0 to z=19.92 (Fragos+, 2013)
J/ApJ/764/41 : X-ray binary evolution across cosmic time (Fragos+, 2013)
J/ApJ/825/7 : Evolution of ∼6Ms CDF-S galaxies (Lehmer+, 2016)
J/AJ/155/81 : Diffuse X-ray-emitting gas in major mergers (Smith+, 2018)
J/ApJS/243/3 : Chandra observations of SINGS galaxies (Lehmer+, 2019)
J/AJ/158/169 : Gas exhaust of starburst engines in mergers (Smith+, 2019)
J/MNRAS/498/4790 : Ultralum. X-ray sources in local Universe (Kovlakas+, 2020)
J/ApJ/907/17 : HMXB-dominant galaxy sample and properties (Lehmer+, 2021)
http://wwwmpa.mpa-garching.mpg.de/SDSS/DR7/ : MPA-JHU DR7 homepage
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 A18 --- Name Adopted galaxy designation
(JHHMMSS.s+DDMMSS.s)
20- 21 I2 h RAh Hour of Right Ascension (J2000) (1)
23- 24 I2 min RAm Minute of Right Ascension (J2000) (1)
26- 29 F4.1 s RAs Second of Right Ascension (J2000) (1)
31 A1 --- DE- Sign of the Declination (J2000) (1)
32- 33 I2 deg DEd Degree of Declination (J2000) (1)
35- 36 I2 arcmin DEm Arcminute of Declination (J2000) (1)
38- 41 F4.1 arcsec DEs Arcsecond of Declination (J2000) (1)
43- 46 F4.2 10+16m-2 NHgal [0.9/5] Galactic column density,
in 10+20cm-2 (2)
48- 52 F5.1 Mpc Dist [187.6/452.4] Adopted distance
54- 58 F5.2 arcsec amaj [3.4/13] Extraction region, semi-major axis
or radius
60- 63 F4.2 arcsec bmin [1.9/7]? Extraction region, semi-minor axis
if elliptical
65- 67 I3 deg PA [0/254]? Extraction region, position angle
(E of N) if elliptical
69- 72 F4.2 [Msun] logMs [7.9/9.4] Log, galactic stellar mass (3)
74- 77 F4.2 [Msun] E_logMs [0.04/0.2] Upper uncertainty in logMstar
79- 82 F4.2 [Msun] e_logMs [0.04/0.2] Lower uncertainty in logMstar
84- 88 F5.2 Msun/yr SFR [0.4/15.4] Star formation rate (3)
90- 93 F4.2 Msun/yr E_SFR [0.03/0.9] Upper uncertainty in SFR
95- 98 F4.2 Msun/yr e_SFR [0.03/0.7] Lower uncertainty in SFR
100- 103 F4.2 [-] O/H [8.1/8.2] Adopted estimate, average oxygen
abundance (4)
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Note (1): Right ascension and declination of the center of the extraction
circle or ellipse.
Note (2): Galactic column density based on the colden tool in CIAO.
Note (3): Galactic stellar mass and star-formation rate based on our SED
fitting results.
Note (4): Adopted estimate of the average oxygen abundances, 12+log(O/H).
For consistency with other studies of XRB scaling relations that include
metallicity, we have converted all abundances to the
Pettini & Pagel (PP04; 2004MNRAS.348L..59P 2004MNRAS.348L..59P) calibration based on the
ratio ([OIII]λ5007/Hβ)/([NII]λ6584/Hα).
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 A18 --- Name Adopted galaxy designation
(JHHMMSS.s+DDMMSS.s)
20- 24 I5 --- ObsID [13013/22513] Chandra ObsID
26- 27 I2 ks Exp [11/24] Exposure time
29- 30 I2 ct Scnts [2/53] Total 0.5-8keV counts (5)
32- 35 F4.1 ct Bcnts [1/13] Estimated 0.5-8keV background
counts, Section 4.1
37- 40 F4.2 ct Acnst [0.03/4.6] Best-fit constant scaling
factor (6)
42- 45 F4.2 ct E_Acnst [0.2/2.1] Upper uncertainty in Acnst (7)
47- 50 F4.2 ct e_Acnst [0.03/2] Lower uncertainty in Acnst (7)
52- 54 I3 --- Csrc [22/167] C-statistic, best-fit source model
56- 58 I3 --- Csrc-exp [38/173] Expected value of the C
statistic (8)
60- 62 I3 --- Csrc-var [276/376] Variance of expected value of C
statistic (8)
64- 68 F5.3 --- Psrc [0.06/1] Null-hypothesis probability,
source model (9)
70- 74 F5.1 10-19W/m2 Fx [0.9/195] Model 0.5-8keV fluxes,
10-16erg/cm2/s
76- 79 F4.1 10-19W/m2 E_Fx [10/49] Upper uncertainty in Fx (7)
81- 84 F4.1 10-19W/m2 e_Fx [0.9/42] Lower uncertainty in Fx (7)
86- 90 F5.1 10+32W Lx [0.8/312] Model 0.5-8keV luminosities,
1039erg/s
92- 95 F4.1 10+32W E_Lx [8/63] Upper uncertainty in Lx (7)
97- 100 F4.1 10+32W e_Lx [0.8/57] Lower uncertainty in Lx (7)
102- 104 I3 --- Cgl [28/174] C-statistic, best-fit global model
106- 108 I3 --- Cgl-exp [50/144] Expected value of the C
statistic (8)
110- 112 I3 --- Cgl-var [295/374] Variance of expected value of C
statistic (8)
114- 118 F5.3 --- Pgl [0.004/1] Null-hypothesis probability,
global model (9)
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Note (5): Total 0.5-8keV counts extracted from the apertures (Table 1)
Note (6): Best-fit constant scaling for the fixed spectral-shape model
(Sec. 5.2)
Note (7): 16-84% confidence interval
Note (8): Expected value of the C statistic and its variance, respectively,
appropriate for the best-fit model.
See methodology in Bonamente M. 2020JApSt..47.2044B 2020JApSt..47.2044B
Note (9): Null-hypothesis probability, which we define here as the integral
of the Csrc-exp distribution from C to infinity
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 F5.2 [0.1nm] logWave [-0.5/4.1] Log, wavelength, Angstrom
7- 11 F5.2 [keV] logE [-3/1.6] Log, Energy
13- 16 I4 10+33W.yr/Msun ELE1-st [0/1078] Emergent SED, Stellar
component (1)
18- 23 F6.4 10+33W.yr/Msun ELE1-gas [0/0.5] Emergent SED, Hot gas (1)
25- 30 F6.4 10+33W.yr/Msun ELE1-HMXB [0/0.9] Emergent SED, HMXB (1)
32- 35 I4 10+33W.yr/Msun ELE1-tot [0/1080] Emergent SED, Total (1)
37- 40 I4 10+33W.yr/Msun ELE2-st [0/2611] Intrinsic SED, Stellar
component (1)
42- 47 F6.4 10+33W.yr/Msun ELE2-gas [0/9.93] Intrinsic SED, Hot gas (1)
49- 54 F6.4 10+33W.yr/Msun ELE2-HMXB [0/0.82] Intrinsic SED, HMXB (1)
56- 59 I4 10+33W.yr/Msun ELE2-tot [0/2610] Intrinsic SED, Total (1)
--------------------------------------------------------------------------------
Note (1): ELE/SFR (1040erg/s (Msun/yr)-1)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 19-Mar-2024