J/ApJ/826/24 Water masers in M31. I. Recombination lines (Darling+, 2016)
Water masers in the Andromeda galaxy.
I. A survey for water masers, ammonia, and hydrogen recombination lines.
Darling J., Gerard B., Amiri N., Lawrence K.
<Astrophys. J., 826, 24-24 (2016)>
=2016ApJ...826...24D 2016ApJ...826...24D (SIMBAD/NED BibCode)
ADC_Keywords: Masers ; Interstellar medium ; Infrared sources ; Radio lines
Keywords: galaxies: individual: M31; galaxies: ISM; ISM: molecules;
Local Group; masers; radio lines: galaxies
Abstract:
We report the results of a Green Bank Telescope survey for water
masers, ammonia (1,1) and (2,2), and the H66α recombination line
toward 506 luminous compact 24µm emitting regions in the Andromeda
Galaxy (M31). We include the 206 sources observed in the Darling water
maser survey for completeness. The survey was sensitive enough to
detect any maser useful for ∼10µas/yr astrometry. No new water
masers, ammonia lines, or H66α recombination lines were detected
individually or in spectral stacks reaching rms noise levels of ∼3mJy
and ∼0.2mJy, respectively, in 3.1-3.3km/s channels. The lack of
detections in individual spectra and in the spectral stacks is
consistent with Galactic extrapolations. Contrary to previous
assertions, there do not seem to be any additional bright water masers
to be found in M31. The strong variability of water masers may enable
new maser detections in the future, but variability may also limit the
astrometric utility of known (or future) masers because flaring masers
must also fade.
Description:
We constructed a catalog of 506 unresolved 24um sources from the
Spitzer 24um map of M31 (Gordon et al. 2006ApJ...638L..87G 2006ApJ...638L..87G); see Figure 1.
Darling (2011ApJ...732L...2D 2011ApJ...732L...2D) observed 206 24um sources in M31 using
the Green Bank Telescope (GBT) in 2010 October through December. The
616-523 22.23508GHz ortho-water maser line observations were
reported in Darling (2011ApJ...732L...2D 2011ApJ...732L...2D), but simultaneous
observations of the para-ammonia (NH3) rotational ground-state
inversion transitions in the metastable states (J,K)=(1,1) and (2,2)
at 23.6945 and 23.72263GHz, respectively, and the hydrogen
recombination line H66α at 22.36417GHz were not. We subsequently
observed all four of these lines toward an additional 300 24um sources
in 2011 October through 2012 January.
The resolution of the 24um Spitzer image is 6" (Gordon et al.
2006ApJ...638L..87G 2006ApJ...638L..87G), so the unresolved IR sources remained within the
33" GBT beam even during the largest pointing drifts. The 33" beam
(FWHM) at 22GHz spans 125pc in M31.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 45 506 M31 line survey results
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See also:
J/ApJ/826/136 : Water masers in M31. II. Multiwavelength data (Amiri+, 2016)
J/MNRAS/418/1689 : Red MSX water maser and ammonia emissions (Urquhart+, 2011)
J/ApJ/741/110 : The BGPS. VII. Massive star-forming regions (Dunham+, 2011)
J/ApJ/687/230 : Survey of M31 with Spitzer (Mould+, 2008)
J/A+A/476/1161 : Spitzer photometry of M33 (Verley+, 2007)
J/MNRAS/369/120 : Kinematic survey of PNe in M31 (Merrett+, 2006)
J/A+AS/101/153 : Galactic H2O masers (Palagi+ 1993)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- Name Object name (HHMMSS.s+DDMMSS.s; J2000)
19 A1 --- f_Name [abm] Flag on Name (1)
21- 23 F3.1 mJy H2O [0.7/4.8] H2O rm noise value (2)
25- 27 F3.1 mJy NH3-1 [0.6/5.1] NH3 (1,1) rms noise value (2)
29- 31 F3.1 mJy NH3-2 [0.6/4.8] NH3 (2,2) rms noise value (2)
33- 35 F3.1 mJy H66a [0.5/4.5] H66α rms noise value (2)
37- 40 I4 km/s Vobs [-500/-100] The observed central velocity
tuning of the 632-674km/s (50MHz) bandwidth (3)
42- 45 I4 km/s VCO [-582/-31]? CO velocity (3)(4)
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Note (1): Flag as follows:
m = Detected H2O maser regions
a = Giant star identified by Amiri & Darling (Paper II, 2016, J/ApJ/826/136).
b = Planetary nebula identified by Merrett et al. (2006, J/MNRAS/369/120).
Note (2): The rms noise is quoted per 3.1-3.3km/s (244kHz) channels.
Note (3): All velocities are in the heliocentric reference frame using the
optical definition.
Note (4): VCO uncertainties are typically ∼1km/s (Nieten+ 2006A&A...453..459N 2006A&A...453..459N),
but the CO velocity map shows mean and median dispersions of 19 and
13km/s within the GBT beam.
Every object was manually inspected in the
Nieten+ (2006A&A...453..459N 2006A&A...453..459N) CO velocity map to ensure that no mask
edges, incomplete data, or high (instrumental) velocity dispersion
regions were included in the stack. All objects in Table 1 that show
a CO velocity can be considered reliable (see section 3).
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History:
From electronic version of the journal
References:
Darling J. 2011ApJ...732L...2D 2011ApJ...732L...2D
Amiri & Darling Paper II. 2016ApJ...826..136A 2016ApJ...826..136A Cat. J/ApJ/826/136
(End) Emmanuelle Perret [CDS] 27-Sep-2016