J/ApJ/804/79 HST/COS observations of QSOs within 600kpc of M31 (Lehner+, 2015)
Evidence for a massive, extended circumgalactic medium around
the Andromeda galaxy.
Lehner N., Howk J.C., Wakker B.P.
<Astrophys. J., 804, 79 (2015)>
=2015ApJ...804...79L 2015ApJ...804...79L
ADC_Keywords: Galaxies, nearby ; Spectra, ultraviolet ; QSOs
Keywords: galaxies: halos; galaxies: individual: M31;
intergalactic medium; Local Group; quasars: absorption lines
Abstract:
We demonstrate the presence of an extended and massive circumgalactic
medium (CGM) around Messier 31 using archival HST Cosmic Origins
Spectrograph ultraviolet spectroscopy of 18 QSOs projected within two
virial radii of M31 (Rvir=300kpc). We detect absorption from SiIII
at -300≲VLSR≲-150km/s toward all three sightlines at R≲0.2Rvir,
3 of 4 sightlines at 0.8≲R/Rvir≲1.1, and possibly 1 of 11 at
1.1<R/Rvir≲1.8. We present several arguments that the gas at these
velocities observed in these directions originates from the M31 CGM
rather than the Local Group or Milky Way CGM or Magellanic Stream. We
show that the dwarf galaxies located in the CGM of M31 have very
similar velocities over similar projected distances from M31. We find
a non-trivial relationship only at these velocities between the column
densities (N) of all the ions and R, whereby N decreases with
increasing R. At R<0.8Rvir, the covering fraction is close to unity
for Si III and C IV (fc∼60%-97% at the 90% confidence level), but
drops to fc≲10%-20% at R≳Rvir. We show that the M31 CGM gas is
bound, multiphase, predominantly ionized, and is more highly ionized
gas at larger R. We estimate using Si II, Si III, and Si IV, a CGM
metal mass of ≳2x106M☉ and gas mass of
≳3x109(Z☉/Z)M☉ within 0.2Rvir, and possibly a factor
of ∼10 larger within Rvir, implying substantial metal and gas masses
in the CGM of M31.
Description:
In the HST Cosmic Origins Spectrograph (COS) archive at the Mikulski
Archive for Space Telescopes (MAST), we identify 31 targets at
projected distances R<2Rvir from M31 that were observed with the COS
G130M and/or G160M gratings (Rλ∼16000). In Table 1, we
summarize the 18 sightlines that are included in the adopted sample
and the 13 sightlines rejected for the main analysis of the M31
circumgalactic medium (CGM) absorption.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 69 31 Sample of COS G130M-G160M targets piercing
the circumgalactic medium (CGM) of M31
table2.dat 90 100 Kinematics and column densities
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See also:
J/A+A/567/A71 : M31 Herschel images (Viaene+, 2014)
J/MNRAS/445/2061 : Absorption in multiphase CGM (Liang+, 2014)
J/ApJ/770/138 : Metallicities of Lyman limit systems and DLA (Lehner+, 2013)
J/ApJ/758/133 : Metallicity profile of M31 HII region & PN (Sanders+, 2012)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJ/749/157 : FUV spectra of Galactic corona sight lines (Wakker+, 2012)
J/ApJ/745/156 : M31 Cepheids with HST/WFC3 (Riess+, 2012)
J/ApJ/740/91 : Lyα & OVI in galaxies around QSOs (Prochaska+, 2011)
J/MNRAS/415/1105 : Intermediate high-velocity clouds distances (Smoker+, 2011)
J/ApJ/727/46 : Highly ionized plasmas in the Milky Way (Lehner+, 2011)
J/ApJ/714/1521 : Spectroscopy of galaxies around distant QSOs (Chen+, 2010)
J/MNRAS/399/728 : UV-bright sources behind M31 halo (Fittingoff+, 2009)
J/ApJ/703/614 : UV star-forming regions in M31 (Kang+, 2009)
J/ApJ/702/940 : Radio and UV spectra of HVC toward the MC (Lehner+, 2009)
J/ApJ/700/1299 : Gas-phase element depletions in the ISM (Jenkins, 2009)
J/ApJS/182/378 : HI and OVI absorbers in nearby Universe (Wakker+, 2009)
J/ApJS/168/213 : Ionization states and cooling efficiencies (Gnat+, 2007)
J/ApJS/163/282 : Molecular hydrogen column densities (Wakker+, 2006)
J/A+A/417/421 : WSRT wide-field HI survey. II. (Braun+, 2004)
J/ApJS/146/125 : O VI in the galactic halo (Savage+, 2003)
J/ApJS/146/1 : O VI absorption in FUSE survey (Wakker+, 2003)
J/ApJS/136/463 : Distances and metallicities of HVCs and IVCs (Wakker, 2001)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1 A1 --- Set [R] R=rejected sample (1)
3- 26 A24 --- Name Target name
28- 34 F7.3 deg RAdeg Right ascension in decimal degrees (J2000)
36- 42 F7.3 deg DEdeg Declination in decimal degrees (J2000)
44- 48 F5.3 --- zem [0.009/2.7] Emission redshift
50- 52 I3 kpc R [25/527] Planar distance from M31 center
54- 64 A11 --- Inst COS instrument
66- 67 I2 --- S/N [0/24] Signal to noise ratio
69 I1 --- Note [2/9]? Rejection reason (2)
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Note (1): if blank = adopted sample. All the targets in the adopted sample
satisfied the following criteria:
* S/N ≳ 5 in at least one transition,
* there is no obvious contamination in the -300≤vLSR≤-150km/s
component from the Magellanic Stream in the direction of the target.
Note (2): Code as follows:
2 = Weak absorption features are observed between -300 and -180km/s in the
profiles of CII, SiII, SiIII, and SiIV, but there is no match in the
velocity centroids between all the observed transitions (including for
the SiIV doublet), implying that there is some contamination from
unrelated absorbers for several of the observed transitions.
3 = These data have too low S/Ns.
4 = Two absorption components at -290 and -210km/s, but at this R.A., decl.,
both are more likely to have a Magellanic Stream origin.
5 = Smeared absorption lines owing to the extended background object.
6 = This sightline pierces the Magellanic Stream (MS) and has a MS component
centered at -300km/s that extends from -400 to -190km/s.
7 = Only CIV is available and both transitions of the doublet are contaminated.
8 = Absorption is observed at -250km/s in SiIII and CIV, but at this R.A.,
decl., it is likely from the Magellanic Stream (MS) (this sightline is
about 20° off the MS body).
9 = This sightline pierces the Magellanic Stream (MS) and has a MS component
centered at -250km/s that extends from -350 to -150km/s.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Name QSO identifier
25- 27 I3 kpc R [25/527] Planar distance from M31 center
29- 34 F6.1 km/s <Vlsr> [-274.3/-204.1]? Average LSR velocity (1)
36- 38 F3.1 km/s e_<Vlsr> ? The 1σ uncertainty in <Vlsr>
40- 45 A6 --- El Species identifier (2)
47- 50 I4 0.1nm lambda Species wavelength (Å)
52- 55 I4 km/s v1 [-321/-260] Lower LSR velocity (3)
57- 60 I4 km/s v2 [-220/-130] Upper LSR velocity (3)
62- 67 F6.1 km/s [-274.3/-188.7]? Average LSR velocity from
the first moment
68 A1 --- u_ Uncertainty flag on due to blending
70- 73 F4.1 km/s e_ [0.8/15.5]? Uncertainty in
75- 78 A4 --- l_logN [≤> ] Limit flag on logN (4)
80- 84 F5.2 [cm-2] logN [12.1/14.6] Log column density in Species
85 A1 --- u_logN Uncertainty flag on logN due to blending
87- 90 F4.2 [cm-2] e_logN [0.01/0.2]? Uncertainty in logN
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Note (1): When more than one transition is detected, is the average
velocity between all the ions (observed with COS) where the detection
is not blended or uncertain.
Note (2): For the O VI, the errors are dominated by systematics from the
correction of the H2 contamination.
Note (3): of the integration of the apparent optical depth (AOD) profile
(method described by Savage & Sembach 1991ApJ...379..245S 1991ApJ...379..245S).
Note (4): Meaning of limit flags:
* "<" indicates that no absorption is detected and a 3σ upper
limit is reported.
* ">" sign is lower limit because the absorption reaches the zero-flux level
* "≤" sign indicates that only one transition of one ion is detected;
this sign emphasizes that the line could be contaminated.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 04-Aug-2015