J/ApJ/745/173 UV absorption sight lines of LMC and SMC (Welty+, 2012)
Interstellar H I and H2 in the Magellanic Clouds: an expanded sample based on
ultraviolet absorption-line data.
Welty D.E., Xue R., Wong T.
<Astrophys. J., 745, 173 (2012)>
=2012ApJ...745..173W 2012ApJ...745..173W
ADC_Keywords: Magellanic Clouds ; Interstellar medium ; Ultraviolet
Keywords: galaxies: ISM - ISM: abundances - Magellanic Clouds - ultraviolet: ISM
Abstract:
We have determined column densities of H I and/or H2 for sight lines
in the Magellanic Clouds from archival Hubble Space Telescope and
Far-Ultraviolet Spectroscopic Explorer spectra of H I Lyα and
H2Lyman-band absorption. Together with some similar data from the
literature, we now have absorption-based N(H I) and/or N(H2) for 285
Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) sight
lines (114 with a detection or limit for both species) - enabling more
extensive, direct, and accurate determinations of molecular fractions,
gas-to-dust ratios, and elemental depletions in these two nearby,
low-metallicity galaxies. For sight lines where the N(H I) estimated
from 21 cm emission is significantly higher than the value derived
from Lyα absorption (presumably due to emission from gas beyond
the target stars), integration of the 21 cm profile only over the
velocity range seen in Na I or H2absorption generally yields much
better agreement. Conversely, N(21 cm) can be lower than N(Lyα)
by factors of 2-3 in some LMC sight lines - suggestive of small-scale
structure within the 21 cm beam(s) and/or some saturation in the
emission. The mean gas-to-dust ratios obtained from N(Htot)/E(B-V)
are larger than in our Galaxy, by factors of 2.8-2.9 in the LMC and
4.1-5.2 in the SMC - i.e., factors similar to the differences in
metallicity. The N(H2)/E(B-V) ratios are more similar in the three
galaxies, but with considerable scatter within each galaxy. These data
may be used to test models of the atomic-to-molecular transition at
low metallicities and predictions of N(H2) based on comparisons of
21 cm emission and the IR emission from dust.
Description:
The HST data for the HI Lyα absorption lines analyzed in this
survey were obtained under various observing programs, with effective
spectral resolutions at Lyα ranging from 0.011Å (2.75km/s)
for Space Telescope Imaging Spectrograph (STIS)/E140H to ∼1.2Å
(∼300km/s) for STIS/G140L. The pipeline-processed spectra were
retrieved from the MAST archive.
Far-UV spectra of nearly 300 LMC and SMC targets are available through
the FUSE Magellanic Clouds Legacy Project (Blair et al. 2009,
Cat. J/PASP/121/634). The FUSE data for HI Lyβ and H2
absorption, for sight lines exhibiting strong Magellanic Clouds H2
absorption in the J=0 and 1 lines of the strongest Lyman bands, were
retrieved from the Legacy Program Web site.
Several surveys of HI 21cm emission from the Magellanic Clouds are now
available (see section 2.2 for the list).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 123 126 SMC sight lines
table2.dat 123 159 LMC sight lines
refs.dat 156 58 References
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
II/236 : UBVR CCD survey of the Magellanic clouds (Massey+, 2002)
II/187 : 30 Doradus OB Associations (Parker 1992)
V/13 : Probable Members of the SMC (Azzopardi+ 1975, 1979)
III/147 : Studies of LMC stellar content (Rousseau+ 1978)
J/PASP/121/634 : FUSE observations in Magellanic Clouds (Blair+, 2009)
J/A+A/456/623 : VLT-FLAMES survey of massive stars (Evans+, 2006)
J/AJ/121/891 : UBV photometry of LMC OB associations (Parker+, 2001)
J/AJ/119/2214 : Photometry of Magellanic OB associations (Massey+, 2000)
J/MNRAS/306/279 : UBV photometry of LMC fg stars III (Schmidt-Kaler+ 1999)
J/AJ/117/206 : LMC far-ultraviolet imaging (Brosch+, 1999)
J/AJ/117/2244 : HST color-magnitude diagrams of the LMC (Olsen, 1999)
J/AJ/118/1684 : UBV photometry of 4 LMC compact OB groups (Walborn+, 1999)
J/AJ/103/1205 : Stellar Content of LH 9 and 10 in the LMC (Parker+ 1992)
J/A+AS/30/261 : UBV and RVs of SMC Supergiants (Ardeberg+, 1977)
Byte-by-byte Description of file: table[12].dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Star ? Star name
16- 21 A6 --- OName ? Other name (1)
23 A1 --- Reg [2w]? Region (2=LMC2;
w=stars in "wing" region of SMC)
25- 26 I2 h RAh Right ascension J2000 (hours)
28- 29 I2 min RAm Right ascension J2000 (min)
31- 34 F4.1 s RAs Right ascension J2000 (sec)
36 A1 --- DE- [-] Declination J2000 (sign)
38- 39 I2 deg DEd Declination J2000 (deg)
41- 42 I2 arcmin DEm Declination J2000 (arcmin)
44- 45 I2 arcsec DEs Declination J2000 (arcsec)
47- 51 F5.2 mag Vmag [9.5/21.6]? V-band magnitude (2)
53- 57 F5.2 mag B-V [-0.3/0.5]? B-V color index (2)
59- 62 F4.2 mag E(B-V)t [0/0.8]? E(B-V) (total) (3)
64- 68 F5.2 mag E(B-V)L [-0.1/0.8]? E(B-V) (LMC) (3)
70- 82 A13 --- SpT ? MK spectral type
84- 85 I2 --- r_SpT ? Reference for SpT (see refs.dat file)
87 A1 --- l_N(HI) Limit flag on N(HI)
88- 92 F5.2 [cm-2] N(HI) ? log(column density) from Lyman-α or
Lyman-β absorption
94- 95 I2 --- r_N(HI) ? Reference for N(HI) (see refs.dat file)
97 A1 --- l_N(H2) Limit flag on N(H2)
98-102 F5.2 [cm-2] N(H2) ? log(H2 column density) from Lyman-band
absorption
103-105 A3 --- f_N(H2) Flags about N(H2) uncertainty (4)
107-109 I3 K T01 ? H2 rotational temperature T01(H2)
from N(J=1)/N(J=0)
111-112 I2 --- r_N(H2) ? Reference for N(H2) (see refs.dat file)
114 A1 --- l_N21 Limit flag on N21
115-119 F5.2 [cm-2] N21 ? log(HI column density) from 21cm emission
(ATCA+Parkes)
121-123 I3 K Tpk [3/158]? Peak 21cm brightness temperature
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Note (1): In table1, AzV number from Azzopardi & Vigneau, Cat. V/13.
In table2, HD or BI (BRUNET+Imbert, 1975A&AS...21..109B 1975A&AS...21..109B) number
Note (2): Origin of photometry:
* Photometry in table 1 is from Massey (2002, Cat. II/236) or
Parker et al. (1992, Cat. J/AJ/103/1205) (preferred) or from
Dachs (1970A&A.....9...95D 1970A&A.....9...95D); Azzopardi et al. (1975, Cat. V/13);
Ardeberg & Maurice (1977, Cat. J/A+AS/30/261);
Isserstedt (1978A&AS...33..193I 1978A&AS...33..193I); Ardeberg (1980A&AS...42....1A 1980A&AS...42....1A);
Bouchet et al. (1985A&A...149..330B 1985A&A...149..330B);
Gordon et al. (2003ApJ...594..279G 2003ApJ...594..279G);
Lennon et al. (2003A&A...398..455L 2003A&A...398..455L);
and/or Evans et al. (2006, Cat. J/A+A/456/623).
* Photometry in table 2 is from Massey (2002, Cat. II/236) or
Parker (1993, Cat. II/187) (preferred) or from
Ardeberg et al. 1972A&AS....6..249A 1972A&AS....6..249A);
Brunet et al. (1975A&AS...21..109B 1975A&AS...21..109B);
Isserstedt (1975A&AS...19..259I 1975A&AS...19..259I, 1979A&AS...38..239I 1979A&AS...38..239I, 1982A&AS...50....7I 1982A&AS...50....7I);
Feitzinger & Isserstedt (1983A&AS...51..505F 1983A&AS...51..505F);
Schmidt-Kaler et al. (1999, Cat. J/MNRAS/306/279); and/or other refs.
Note (3): Origin of intrinsic colors:
* in table 1: Using intrinsic colors of FitzGerald (1970A&A.....4..234F 1970A&A.....4..234F)
and assuming a Galactic contribution of 0.03-0.04 mag.
* in table 2: E(B-V) is calculated using the intrinsic colors of
FitzGerald (1970A&A.....4..234F 1970A&A.....4..234F) or (for WR stars) from P. Crowther
(priv. comm.); the Galactic foreground extinction is estimated from
Fig. 13 of Staveley-Smith et al. (2003MNRAS.339...87S 2003MNRAS.339...87S).
Note (4): Flag as follows:
mod = moderate H2 (N likely <1018cm-2)
wk = weak H2 (N likely <1016cm-2)
ul = upper limit (N likely <1015cm-2)
: = uncertainty flag
Values given as mod, wk, or ul are from unmeasured FUSE data.
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Ref Reference code
4- 22 A19 --- BibCode Bibcode
24- 48 A25 --- Aut Author's name(s)
51-205 A155 --- Comm Comment
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 01-Aug-2013