J/AJ/143/145 Emission-line objects from ALFALFA Hα survey (Kellar+, 2012)
Hα dots: a catalog of faint emission-line objects discovered in
narrowband images.
Kellar J.A., Salzer J.J., Wegner G., Gronwall C., Williams A.
<Astron. J., 143, 145 (2012)>
=2012AJ....143..145K 2012AJ....143..145K
ADC_Keywords: Spectroscopy ; Redshifts ; Galaxies, Seyfert ; QSOs ;
Abundances, [Fe/H] ; Equivalent widths
Keywords: galaxies: abundances - galaxies: dwarf - galaxies: starburst - surveys
Abstract:
During a wide-field narrowband Hα imaging survey, we noted the
presence of numerous isolated emission-line point sources in the data.
These objects could represent ultra-low-luminosity galaxies at
low-redshift (detection via Hα), isolated extragalactic HII
regions associated with the galaxy targeted by the original
observation, or background galaxies or QSOs where strong emission
lines (most often [OIII]λ5007) redshift into our narrowband
filter. We have carried out a systematic search for these "Hα
dots" in over 200 15x15arcmin fields. To date we have cataloged 61
candidate emission-line sources in roughly 11.7deg2. The sample has
a median R magnitude of 19.5, and detects objects as faint as R=22.6.
Follow-up spectroscopy reveals that ∼85% of the candidates are bona
fide emission-line objects, with roughly 60% of the real sources being
lower-redshift objects (detection via Hα) and 40% being
higher-redshift objects detected via [OIII] emission or some other
emission line. Here we present the results of our initial survey and
follow-up spectroscopy. We use our sample to study the properties
(including star-formation rates and metal abundances) of
low-luminosity star-forming galaxies in the nearby universe and of
low-metallicity star-forming galaxies at z∼0.33.
Description:
Our ALFALFA Hα galaxy sample has been selected from the catalog
of HI-detected sources found by the ALFALFA survey, a blind 21cm radio
survey being carried out with the 305m Arecibo radio telescope. The
data used for our Hα dot survey were acquired as part of the
ALFALFA Hα survey (Sugden et al., 2008AAS...212.1905S 2008AAS...212.1905S; Salzer et
al. 2012, in preparation).The ALFALFA Hα observations consist of
images taken through both a continuum R-band filter and a set of
narrowband Hα filters with the WIYN 0.9m telescope at Kitt Peak
National Observatory. We ran our search software on the narrowband
Hα images obtained between 2006 March and 2007 October.
Spectra of most of the Hα dot candidates presented in Table 2
were obtained using the MDM Hiltner 2.4m telescope at the MDM
Observatory in 2007 November and 2008 March. The spectra were acquired
using the CCDS spectrograph covering the entire optical spectrum from
3720Å to 7300Å, centered at 5400Å.
Additional spectra for Hα dot candidates were obtained with the
9.2m Hobby-Eberly Telescope (HET) between 2008 August and 2011
January. Observations were acquired using the Marcario Low Resolution
Spectrograph.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 61 61 Hα dot candidates-observed properties
table3.dat 69 61 Spectroscopic results
table4.dat 41 52 Derived quantities
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See also:
VIII/77 : HI spectral properties of galaxies (Springob+, 2005)
J/AJ/143/133 : Properties of dwarf galaxies from the ALFALFA survey
(Huang+, 2012)
J/A+A/545/A16 : Halpha3. Catalog and SFR in Virgo cluster (Gavazzi+, 2012)
J/AJ/142/170 : ALFALFA survey: the α.40 HI source catalog
(Haynes+, 2011)
J/AJ/139/279 : Outlying HII regions in HI-selected galaxies (Werk+, 2010)
J/AJ/138/338 : Arecibo Legacy Fast ALFA Survey. IX. (Stierwalt+, 2009)
J/ApJS/178/247 : Hα and [NII] survey in local 11Mpc (Kennicutt+, 2008)
J/ApJS/173/538 : XUV-Disk galaxies in the Local Universe (Thilker+, 2007)
J/ApJ/668/853 : Spectroscopy of UltraStrong Emission Line galaxies
(Kakazu+, 2007)
J/ApJS/165/307 : Survey for ionization in neutral gas galaxies. I.
(Meurer+, 2006)
J/AJ/130/2571 : KISS Hα-selected survey list 3 (Jangren+, 2005)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Dot [1/61] Hα dot candidate number
<[KSW2012] NNN> in Simbad (G1)
3 A1 --- f_Dot [s] Multiple detections (G2)
5- 6 I2 h RAh Hour of Right Ascension (J2000)
8- 9 I2 min RAm Minute of Right Ascension (J2000)
11- 14 F4.1 s RAs Second of Right Ascension (J2000)
16 A1 --- DE- Sign of the Declination
17- 18 I2 deg DEd Degree of Declination (J2000)
20- 21 I2 arcmin DEm Arcminute of Declination (J2000)
23- 26 F4.1 arcsec DEs Arcsecond of Declination (J2000)
28- 32 F5.2 mag Dmag Difference between the instrumental R and
Hα magnitudes (1)
34- 38 F5.2 --- Ratio Ratio of the magnitude difference Dmag to the
magnitude difference error (2)
40- 44 F5.3 10-17W/m2 Flux The measured emission-line flux as measured
from the continuum-subtracted narrowband
images (in 10-14erg/s/cm2)
46- 50 F5.3 10-17W/m2 e_Flux Error in Flux (in 10-14erg/s/cm2)
52- 56 F5.2 mag Rmag [15.83/22.64] The measured broadband R
magnitude; VEGA system
58- 61 F4.2 mag e_Rmag Error in Rmag
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Note (1): Δm=mHα-mR (see Section 3 and Equation (1) for
more details).
Note (2): ratio=Δm/σΔm (see Section 3 and Equation
(3) for more details).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Dot [1/61] Hα dot candidate number
<[KSW2012] NNN> in Simbad (G1)
3 A1 --- f_Dot [s] Multiple detections (G2)
5- 13 A9 --- ELG Emission-line galaxy type (3)
15- 20 F6.4 --- z ? Spectroscopic redshift, derived from
the average redshift all strong emission
lines (typical uncertainties are 15-30km/s)
22- 26 F5.2 --- cHb ? Decimal reddening coefficient
cHβ, derived from the
Balmer-line ratio Hα/Hβ
28- 32 F5.1 0.1nm W(Ha) ? Equivalent width of the Hα line
34- 38 F5.1 0.1nm W(O3) ? Equivalent width of the [OIII] line
40- 44 F5.2 [---] log(N2/Ha) ? Key reddening-corrected emission-line
ratio log([NII]λ6583/Hα)(4)
45 A1 --- f_log(N2/Ha) [*] Unreliable log([NII]/Ha) (5)
47- 50 F4.2 [---] log(O3/Hb) ? Key reddening-corrected emission-line
ratio log([OIII]λ5007/Hβ)(4)
51 A1 --- f_log(O3/Hb) [*] Unreliable log([OIII]/Hb) (5)
53- 56 F4.2 [---] log(O2/Hb) ? Key reddening-corrected emission-line
ratio log([OII]λ3727/Hβ) (4)
57 A1 --- f_log(O2/Hb) [*] Unreliable log([OII]/Hb) (5)
59- 63 F5.2 [---] log(S2/Ha) ? Key reddening-corrected emission-line
ratio log([SII]λλ6717,
6731/Hα) (4)
64 A1 --- f_log(S2/Ha) [*] Unreliable log([SII]/Ha) (5)
66- 69 F4.2 [Sun] [O/H] ? Metallicity (log(O/H)+12) (see Section 6.2)
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Note (3): Emission-line galaxy type as follows:
SF = Star-forming galaxy (regardless of redshift);
Sy1 = Seyfert 1 galaxy;
Sy2 = Seyfert 2 galaxy;
LINER = Low-ionization nuclear emission region;
QSO = Quasi-stellar object/quasar;
Not ELG = Spectrum does not include any detectable emission features. This
latter class represents false detections in our initial list of
Hα dot candidates. These false detections can only be
recognized as such after a spectrum has been acquired.
Note (4): Objects where one or more of these line ratios are missing
represent targets where the relevant lines were either not measurable
or (most often) redshifted out of the observed spectral region.
Note (5):
* = indicate objects for which cHβ could not be measured or was deemed
unreliable. For these objects the emission-line ratios listed are not
reddening corrected.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Dot ? Hα dot candidate number
<[KSW2012] NNN> in Simbad (G1)
3 A1 --- f_Dot [s] Multiple detections (G2)
5- 11 F7.1 Mpc Dist Distance
13- 18 F6.2 mag RMag ? Absolute R magnitude
20- 24 F5.2 [10-7W] log(LHa) ? The Hα luminosity log(LHα)
(in erg/s) (6)
26- 30 F5.3 Msun/yr SFR ? Star-formation rate (7)
32- 35 I4 km/s DV ? Velocity difference (8)
37- 41 F5.2 Mpc DR ? Physical separation distance (8)
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Note (6): LHα=FHα*4πD2, where FHα is the corrected
Hα flux and D, the distance (see Equation (5) for more details)
Note (7): SFR=7.9*10-42LHα (see Equation (6) for more details)
Note (8): Between each low-redshift Hα-detected object and the ALFALFA
galaxy in the field (see Section 6.3 for more details).
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Global notes:
Note (G1): We use the term Hα dot to describe the emission-line
objects found in our survey. We do not intend for this term to be used
to refer to the entire class of objects that are compact and possess
strong line emission.
The sources are grouped by the ALFALFA Hα observing run from
which the narrowband images originate, and are then ordered by right
ascension within these groups. Hence, objects 1-13 are from the 2006
March ALFALFA Hα run, objects 14-22 from 2006 September, objects
23-28 from 2007 February, objects 29-42 from 2007 May, and and objects
43-61 from 2007 October.
Note (G2):
s = This object, cataloged as both Hα dot 7 and Hα dot 24,
represents independent detections of the same object found in two fields
observed on different observing runs (see Section 4 for more details).
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History:
From electronic version of the journal
(End) Sylvain Guehenneux [CDS] 19-Jul-2013