J/ApJ/950/189 Dwarf Ha em.-line galaxies within voids. I. FN8 (Draper+, 2023)
Searching for dwarf Hα emission-line galaxies within voids.
I. Survey methods and first observations.
Draper C.D., Moody J.W., McNeil S.R., Joner M.D., Steele R., Steele J.
<Astrophys. J., 950, 189 (2023)>
=2023ApJ...950..189D 2023ApJ...950..189D
ADC_Keywords: Galaxies, dwarf; Photometry, H-alpha; Photometry, SDSS;
Intergalactic medium; Equivalent widths; Redshifts
Keywords: Voids ; Mean matter density ; Large-scale structure of the Universe ;
Dwarf galaxies
Abstract:
The population density of dwarf galaxies in low-density voids is
likely determined by the dark matter halo mass function and how galaxy
formation proceeds in smaller halos. This depends on the nature of
dark matter itself, making the dwarf galaxy population a tracer of its
properties. While dwarfs have been found in smaller, closer voids,
they have proven difficult to find in larger, more distant voids
through magnitude-limited spectroscopic surveys. This is because these
surveys detect an overwhelmingly large number of objects behind the
voids that must be verified spectroscopically, making void surveys
prohibitively inefficient and expensive in terms of large-telescope
time. Narrowband imaging for emission lines such as Hα reduces
the number of background objects, although the overall number remains
large. If imaging is done through a filter set with overlapping
transmission wings, then object redshift can be estimated from
photometry alone. The precision possible is an order of magnitude
greater than single-band photometry, with the caveat that the captured
line must be identified through other means. Broadband photometry can
be used to reject enough objects with emission of an unwanted type to
make obtaining spectra of the remaining objects feasible. In this
study, we present an Hα survey for dwarf galaxies with Mr'
fainter than -14mag through the center 4.3 square degrees of the void
FN8. Using Sloan g', r', i' photometry, we exclude enough [OII] and
[OIII] emitters that follow-up spectra of only a few dozen objects are
required to statistically estimate the void population density.
Description:
The survey method described and used here was designed around the
capabilities of the Kitt Peak National Observatory (KPNO) Mayall 4m
telescope, Mosaic 1.1 Wide Field Imager, and available redshifted
Hα filters. KPNO possesses a set of redshifted Ha filters, each
with a bandwidth of approximately 80Å FWHM.
The three filters appropriate for our needs are k1011, k1012, and
k1013, which are centered at 6654.2, 6698.5, and 6730.7Å,
respectively. We refer to them as Ha8, Ha12, and Ha16, with the number
after "Ha" being the approximate shift of the filter center in
nanometers from the rest wavelength of Hα.
See Section 2.
In addition to Hα emission, there are three other prominent
emission lines, [OIII]λλ5007,4959Å (hereafter
[OIII]), and [OII]λ3727Å, (hereafter [OII]), which fall
within the filter bandpasses for background objects at specific
redshifts.
We queried the SDSS DR7 database for galaxies with emission having
0.003<z<0.031 (the range for Ha), 0.31<z<0.35 (the range for [OIII]),
and 0.77<z<0.82 (the range for [OII]). We rejected objects with
magnitude uncertainties greater than 0.2mag in either g', r', or i'.
See Section 3.
On 13-17 of February 2013, we used the KPNO Mayall 4m telescope and
MOSAIC imager to image through the center of a void we designate as
FN8. This void is the first entry in the catalog of
Hoyle & Vogeley (2002ApJ...566..641H 2002ApJ...566..641H) and the eighth entry in the
catalog of Foster & Nelson (2009ApJ...699.1252F 2009ApJ...699.1252F). We took the
coordinates of the center to be RA=12:50,DE=+72.6, cz=5050km/s, which
is the average of the entries in the respective catalogs. The depth of
this void ranges from cz=3140km/s to cz=6960km/s, for a diameter in cz
of 3820km/s.
See Section 4.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table6.dat 54 42 Emission-line candidates in the 1σ region
table7.dat 54 230 Emission-line candidates in the 2σ region
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See also:
I/284 : The USNO-B1.0 Catalog (Monet+ 2003)
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
VII/259 : 6dF galaxy survey final redshift release (Jones+, 2009)
J/AJ/95/1629 : [O III] emission in 2 field-galaxy surveys (Moody+ 1988)
J/PASP/111/438 : Updated Zwicky catalog (UZC) (Falco+, 1999)
J/AJ/118/2561 : Galaxies within prominent nearby voids (Grogin+, 1999)
J/MNRAS/335/712 : R magnitude of cluster of galaxies (Trentham+, 2002)
J/AJ/130/2571 : KISS Hα-selected survey list 3 (Jangren+, 2005)
J/ApJS/176/301 : Subaru/XMM-Newton deep survey IV. (SXDS) (Ouchi+, 2008)
J/AJ/144/16 : Opt. and HI properties of galaxies in voids (Kreckel+, 2012)
J/MNRAS/464/666 : Void Galaxy Survey, photometry and structure (Beygu+, 2017)
J/ApJ/837/42 : N/O ratio of dwarf galaxies from SDSS (Douglass+, 2017)
J/MNRAS/471/629 : Bootes-HiZELS. Em.-line gal. at z=0.4-4.7 (Matthee+, 2017)
J/ApJ/864/144 : N/O and Ne/O ratios of SDSS dwarf galaxies (Douglass+, 2018)
J/MNRAS/476/4725 : SC4K catalogue of candidate LAEs (Sobral+, 2018)
J/AJ/157/99 : Phot. redshifts of emission-line galaxies (Lesser+, 2019)
J/MNRAS/482/4329 : Void galaxies in the nearby Universe (Pustilnik+, 2019)
Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Field Field identifier
8- 12 I5 --- ID [3467/21046] Candidate internal identifier
14- 15 I2 h RAh [12/13] Hour of Right Ascension (J2000)
17- 18 I2 min RAm Minute of Right Ascension (J2000)
20- 25 F6.3 s RAs Second of Right Ascension (J2000)
27 A1 --- DE- [+] Sign of Declination (J2000)
28- 29 I2 deg DEd [71/73] Degree of Declination (J2000)
31- 32 I2 arcmin DEm Arcminute of Declination (J2000)
34- 39 F6.3 arcsec DEs Arcsecond of Declination (J2000)
41- 44 F4.1 mag rmag [20.2/23.8] SDSS r' band apparent AB magnitude
46- 49 I4 0.1nm EW [40/1690] Equivalent width; Angstroms
51- 54 F4.2 --- Depth [0.28/0.81] Depth in void; estimated cz assuming
the emission line is Hα
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Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Field Field identifier
8- 12 I5 --- ID [1560/25585] Candidate internal identifier
14- 15 I2 h RAh [12/13] Hour of Right Ascension (J2000)
17- 18 I2 min RAm Minute of Right Ascension (J2000)
20- 25 F6.3 s RAs Second of Right Ascension (J2000)
27 A1 --- DE- [+] Sign of Declination (J2000)
28- 29 I2 deg DEd [71/73] Degree of Declination (J2000)
31- 32 I2 arcmin DEm Arcminute of Declination (J2000)
34- 39 F6.3 arcsec DEs Arcsecond of Declination (J2000)
41- 44 F4.1 mag rmag [16.1/24.3] SDSS r' band apparent AB magnitude
46- 49 I4 0.1nm EW [10/2000] Equivalent width; Angstroms
51- 54 F4.2 --- Depth [0.1/0.85] Depth in void; estimated cz assuming
the emission line is Hα
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 18-Aug-2025