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 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 60 130 Optical counterpart redshifts of HI-emitting
galaxies
table4.dat 87 62 Ambiguous optical counterparts
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See also:
J/AJ/142/170 : ALFALFA survey: the α.40 HI source catalog (Haynes+, 2011)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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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
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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.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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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)
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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
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 01-Mar-2017