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. =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 H66{alpha} recombination line toward 506 luminous compact 24{mu}m 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 ~10{mu}as/yr astrometry. No new water masers, ammonia lines, or H66{alpha} 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); see Figure 1. Darling (2011ApJ...732L...2D) observed 206 24um sources in M31 using the Green Bank Telescope (GBT) in 2010 October through December. The 6_16_-5_23_ 22.23508GHz ortho-water maser line observations were reported in Darling (2011ApJ...732L...2D), but simultaneous observations of the para-ammonia (NH_3_) 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 H66{alpha} 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), 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: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 45 506 M31 line survey results -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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] H_2_O rm noise value (2) 25- 27 F3.1 mJy NH3-1 [0.6/5.1] NH_3_ (1,1) rms noise value (2) 29- 31 F3.1 mJy NH3-2 [0.6/4.8] NH_3_ (2,2) rms noise value (2) 33- 35 F3.1 mJy H66a [0.5/4.5] H66{alpha} 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) -------------------------------------------------------------------------------- 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), 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) 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). -------------------------------------------------------------------------------- History: From electronic version of the journal References: Darling J. 2011ApJ...732L...2D Amiri & Darling Paper II. 2016ApJ...826..136A Cat. J/ApJ/826/136 ================================================================================ (End) Emmanuelle Perret [CDS] 27-Sep-2016