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J/MNRAS/459/220 Optical redshifts of OH- and HI-emitting galaxies (Suess+, 2016)

Identifying OH imposters in the ALFALFA Neutral Hydrogen Survey. Suess K.A., Darling J., Haynes M.P., Giovanelli R. <Mon. Not. R. Astron. Soc., 459, 220-231 (2016)> =2016MNRAS.459..220S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, radio ; H I data ; Redshifts ; Masers Keywords: line: identification - masers - galaxies: distances and redshifts - galaxies: spiral - galaxies: starburst - radio lines: galaxies Abstract: OH megamasers (OHMs) are rare, luminous molecular masers that are typically observed in (ultra) luminous infrared galaxies and serve as markers of major galaxy mergers. In blind emission line surveys such as the Arecibo Legacy Fast Arecibo L-Band Feed Array (ALFALFA) survey for neutral hydrogen (HI), OHMs at z∼0.2 can mimic z∼0.05 HI lines. We present the results of optical spectroscopy of ambiguous HI detections in the ALFALFA 40 per cent data release detected by the Wide Field Infrared Survey Explorer (WISE) but with uncertain optical counterparts. The optical redshifts, obtained from observations at the Apache Point Observatory, revealed five new OHMs and identified 129 HI optical counterparts. 60 candidates remain ambiguous. The new OHMs are the first detected in a blind spectral line survey. The number of OHMs in ALFALFA is consistent with predictions from the OH luminosity function. Additionally, the mid-infrared magnitudes and colours of the OHM host galaxies found in a blind survey do not seem to differ from those found in previous targeted surveys. This validates the methods used in previous IR-selected OHM surveys and indicates there is no previously unknown OHM-producing population at z∼0.2. We also provide a method for future surveys to separate OH megamasers from 99 per cent of HI line emitters without optical spectroscopy by using WISE infrared colours and magnitudes. Since the fraction of OHMs found in flux-limited HI surveys is expected to increase with the survey's redshift, this selection method can be applied to future flux-limited high-redshift hydrogen surveys. Description: We observed candidate hydroxyl megamasers (OHMs) at the Apache Point Observatory over 15 sessions between 2011 December and 2013 March. Observations were made using the Dual Imaging Spectrograph at the Apache Point Observatory (APO) 3.5m telescope with the B400/R300 grating and a 1.5-arcsec spectroscopic slit. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table3.dat 60 130 Optical counterpart redshifts of HI-emitting galaxies table4.dat 87 62 Ambiguous optical counterparts
See also: J/AJ/142/170 : ALFALFA survey: the α.40 HI source catalog (Haynes+, 2011) Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 17 A17 --- Name Object name 18 A1 --- n_Name [2-6] Note on Name (1) 20- 21 I2 h RAh Optical counterpart right ascension (J2000) 22- 23 I2 min RAm Optical counterpart right ascension (J2000) 24- 28 F5.2 s RAs Optical counterpart right ascension (J2000) 29 A1 --- DE- Optical counterpart declination sign (J2000) 30- 31 I2 deg DEd Optical counterpart declination (J2000) 32- 33 I2 arcmin DEm Optical counterpart declination (J2000) 34- 37 F4.1 arcsec DEs Optical counterpart declination (J2000) 39- 44 A6 --- n_Pos Note on Pos (2) 46- 50 I5 km/s Vopt Optical velocity (uncertainty is 130km/s) 52- 56 I5 km/s VHI ? HI velocity from Haynes et al. (2011, Cat. J/AJ/142/170) 58- 60 I3 km/s e_VHI ? rms uncertainty on VHI
Note (1): 2 Notes as follows: 2 = This spectrum showed both emission and absorption lines. The emission lines were more prevalent, but the offset absorption lines clearly showed in the blue half of the spectrum. Absorption was especially evident in Hβ and blueward Balmer series lines, where broad emission lines were nearly divided in two by the offset absorption. The emission velocity occurred at 5035km/s, a match for the ALFALFA HI line; the absorption lines were offset to 5770km/s. The velocity listed in Table 3 is the emission velocity, which matches the ALFALFA HI velocity. The galaxy exhibits disturbed morphology in SDSS, and the absorption and emission lines may be offset because they come from different nuclei. 3 = This object was identified as a clear HI detection; in SDSS it appears to be a blue compact dwarf galaxy. 4 = The optical counterpart for this object was confirmed to be the blue extended object to the west of the central ALFALFA coordinates. 5 = Two objects were observed within the ALFALFA beam radius. One observed galaxy was to the east of the ALFALFA target coordinates, and one to the south. Both galaxies matched the HI velocity, so the coordinates and measured velocities for both are included in this table. 6 = Most observed objects have at least five identifying spectral lines. For this object, only Hα was identified. Despite the scarcity of observable optical lines in this spectra, we are confident of the HI confirmation. The singular line is bright, shows extension along the spatial axis of the spectrum, and it is very close to the expected HI redshift. In visible light, the object appears to be a low surface brightness galaxy. Note (2): For 249263, East and North optical counterparts.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 17 A17 --- Name Object name 18- 19 A2 --- m_Name [AB: ] Multiplicity index on Name 20 A1 --- n_Name [2-9] Note on Name (1) 22- 23 I2 h RAh Observed right ascension (J2000) 24- 25 I2 min RAm Observed right ascension (J2000) 26- 30 F5.2 s RAs Observed right ascension (J2000) 31 A1 --- DE- Observed declination sign (J2000) 32- 33 I2 deg DEd Observed declination (J2000) 34- 35 I2 arcmin DEm Observed declination (J2000) 36- 39 F4.1 arcsec DEs Observed declination (J2000) 41- 42 A2 --- n_Pos Note on Pos (2) 44- 49 I6 km/s Vopt ? Optical velocity (uncertainty is 130km/s) 52- 56 I5 km/s VHI ? HI velocity from Haynes et al. (2011, Cat. J/AJ/142/170) 58- 59 I2 km/s e_VHI ? rms uncertainty on VHI 61- 66 I6 km/s VOH ? OH velocity 68- 69 I2 km/s e_VOH ? rms uncertainty on VOH 71- 87 A17 --- Com Comments (3)
Note (1): Notes as follows: 2 = Possible pointing error during observations; this object may not be the WISE bright source or the ALFALFA detection. 3 = The α.40 data release of the ALFALFA catalogue incorrectly states that this object is an OHM (Haynes et al., 2011, Cat. J/AJ/142/170). While the measured optical velocity is much higher than the ALFALFA velocity, it does not match the OH velocity and the object's identity remains unknown. 4 = The velocity determination for this object was measured from only one line, presumed to be Hα. 5 = Bleed-in from a nearby star obscured optical lines for this object. 6 = Two objects were observed within beam uncertainty of the ALFALFA detection. The first had no visible optical lines, and the second (the velocity listed in Table 4) showed broad line emission that matched neither the OH nor the HI velocity. 7 = Due to high redshift, this object is likely an AGN. 8 = Guiding errors during observing rendered these frames unusable; no further observations were made. 9 = Two possible optical counterparts were observed. One matched neither OH nor HI velocities, and the other had no clear optical lines. Note (2): A: or B: for HI011145+290458 Note (3): Comments as follows: neither = observed velocity matches neither HI nor OH no lines = objects for which no optical lines were observable and no velocity determination could be made ML = ALFALFA HI detection is a marginal line, likely not a real detections UL = ALFALFA line is uncertain, and could be HI or another line
History: From electronic version of the journal
(End) Patricia Vannier [CDS] 01-Mar-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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