J/ApJ/827/89 HST imaging of Pisces A and B (Tollerud+, 2016)
HST imaging of the local volume dwarf galaxies Pisces A and B:
prototypes for local group dwarfs.
Tollerud E.J., Geha M.C., Grcevich J., Putman M.E., Weisz D.R.,
Dolphin A.E.
<Astrophys. J., 827, 89-89 (2016)>
=2016ApJ...827...89T 2016ApJ...827...89T (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Photometry, HST ; Radial velocities
Keywords: galaxies: distances and redshifts; galaxies: dwarf; Local Group;
methods: statistical
Abstract:
We present observations of the Pisces A and B galaxies with the
Advanced Camera for Surveys on the Hubble Space Telescope. Photometry
from these images clearly resolves a red giant branch (RGB) for both
objects, demonstrating that they are nearby dwarf galaxies. We
describe a Bayesian inferential approach to determining the distance
to these galaxies using the magnitude of the tip of the RGB (TRGB),
and then apply this approach to these galaxies. This reveals the
distance to these galaxies as 5.64-0.15+0.13Mpc and
8.89-0.85+0.75Mpc for Pisces A and B, respectively, placing both
within the Local Volume but not the Local Group (LG). We estimate the
star formation histories of these galaxies, which suggests that they
have recently undergone an increase in their star formation rates.
Together these yield luminosities for Pisces A and B of
MV=-11.57-0.05+0.06 and -12.9±0.2, respectively, and estimated
stellar masses of log(M*/M☉)=7.0-1.7_+0.4 and 7.5-1.8+0.3.
We further show that these galaxies are likely at the boundary between
nearby voids and higher-density filamentary structure. This suggests
that they are entering a higher-density region from voids, where they
would have experienced delayed evolution, consistent with their recent
increased star formation rates. If this is indeed the case, they are
useful for study as proxies of the galaxies that later evolved into
typical LG satellite galaxies.
Description:
The observations of Pisces A and B were taken as part of HST program
GO-13745 (Cycle 22, PI Tollerud, executed 2014 October 30-November 8).
Pisces A and B were observed for a single orbit each with ACS/WFC,
using the F606W and F814W filters.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 265 2 Key properties of pisces A and B
table2.dat 381 56000 Distributions of quantities
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See also:
VII/259 : 6dF galaxy survey final redshift release (Jones+, 2009)
J/A+A/587/L3 : HI datacubes if Pisces A and B (Carignan+, 2016)
J/ApJ/806/95 : A search for ultra-compact HVC counterparts (Sand+, 2015)
J/AJ/144/16 : Optical and HI properties of galaxies in voids (Kreckel+, 2012)
J/AJ/144/4 : Dwarf galaxies data in the Local Group (McConnachie+, 2012)
J/ApJ/653/240 : Low-mass SDSS dwarf galaxy properties (Geha+, 2006)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Object name
10- 11 I2 h RAh Hour of right ascension (J2000)
13- 14 I2 min RAm Minute of right ascension (J2000)
16- 19 F4.1 s RAs Second of right ascension (J2000)
21 A1 --- DE- Sign of declination (J2000)
22- 23 I2 deg DEd Degree of declination (J2000)
25- 26 I2 arcmin DEm Arcminute of declination (J2000)
28- 32 F5.2 arcsec DEs Arcsecond of declination (J2000)
34- 39 F6.2 deg GLAT Galactic latitude
41- 46 F6.2 deg GLON Galactic longitude
48- 51 F4.2 Mpc Dist Distance (section 3)
53- 56 F4.2 Mpc e_Dist Negative uncertainty on Dist
58- 61 F4.2 Mpc E_Dist Positive uncertainty on Dist
62 A1 --- f_Dist [a] Flag on Dist (1)
64- 68 F5.2 mag M-m Distance modulus from Tip of the RGB (TRGB)
70- 73 F4.2 mag e_M-m Negative uncertainty on M-m
75- 78 F4.2 mag E_M-m Positive uncertainty on M-m
79 A1 --- f_M-m [a] Flag on M-m (1)
81- 85 F5.2 mag F814W F814W magnitude of the TRGB (µF814W)
87- 90 F4.2 mag e_F814W Negative uncertainty on F814W
92- 95 F4.2 mag E_F814W Positive uncertainty on F814W
96 A1 --- f_F814W [a] Flag on F814W (1)
98-103 F6.2 mag F606W0 Absolute F606W magnitude (section 4)
105-108 F4.2 mag e_F606W0 Negative uncertainty on F606W0
110-113 F4.2 mag E_F606W0 Positive uncertainty on F606W0
114 A1 --- f_F606W0 [a] Flag on F606W0 (1)
116-121 F6.2 mag F814W0 Absolute F814W magnitude (section 4)
123-126 F4.2 mag e_F814W0 Negative uncertainty on F814W0
128-131 F4.2 mag E_F814W0 Positive uncertainty on F814W0
132 A1 --- f_F814W0 [a] Flag on F814W0 (1)
134-139 F6.2 mag VMag Absolute V-band magnitude (2)
141-144 F4.2 mag e_VMag Negative uncertainty on VMag
146-149 F4.2 mag E_VMag Positive uncertainty on VMag
150 A1 --- f_VMag [a] Flag on VMag (1)
152-155 F4.2 mag V-I V-I color index (2)
157-160 F4.2 mag e_V-I V-I uncertainty
162-166 F5.2 arcsec Reff On-sky major axis half-light radius
from F606W imaging (section 4) in arcsec
168-171 F4.2 arcsec e_Reff Reff uncertainty
173-175 I3 pc reff Physical half-light radius in F606W in pc
177-178 I2 pc e_reff Negative uncertainty on reff
180-181 I2 pc E_reff Positive uncertainty on reff
182 A1 --- f_reff [a] Flag on reff (1)
184-187 F4.2 --- n Sersic Index from F606W imaging (section 4)
189-192 F4.2 --- e_n Negative uncertainty on n
194-197 F4.2 --- E_n Positive uncertainty on n
199-202 F4.2 --- ell Ellipticity in F606W (1-b/a)
204-207 F4.2 --- e_ell ell uncertainty
209-211 I3 deg PA Position angle of major axis in F606W θ
(East of North)
213-215 F3.1 deg e_PA PA uncertainty
217-219 F3.1 [Msun] logM* Total stellar mass as inferred from the CMD (3)
221-223 F3.1 [Msun] e_logM* Negative uncertainty on logM*
225-227 F3.1 [Msun] E_logM* Positive uncertainty on logM*
229-232 F4.1 10+6Msun MHI HI gas mass from GALFA-HI (4)
234-236 F3.1 10+6Msun e_MHI Negative uncertainty on MHI
238-240 F3.1 10+6Msun E_MHI Positive uncertainty on MHI
241 A1 --- f_MHI [a] Flag on MHI (1)
243-245 I3 km/s VelI Systemic heliocentric velocity of HI gas
247-249 F3.1 km/s e_VelI VelI uncertainty
251-254 F4.1 km/s W50HI W50 of HI gas
256-258 F3.1 km/s e_W50HI W50HI uncertainty
260-262 I3 km/s Vel Optival heliocentric velocity (5)
264-265 I2 km/s e_Vel Vel uncertainty
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Note (1):
a = A quantity that has a significantly non-Gaussian distribution. Such
quantities are better represented using the samples from the distributions
given in Table 2.
Note (2): VImagnitude and color, transformed from the HST bands following the
prescription of Sirianni+ (2005PASP..117.1049S 2005PASP..117.1049S), Section 8.3.
Note (3): Total stellar mass (log(M*,SFH/M☉)) as inferred from the CMD
from fitting the SFH following the procedure described in Section 5.
Note (4): HI gas mass from GALFA-HI (Peek+ 2011ApJS..194...20P 2011ApJS..194...20P) as described in
Tollerud+ (2015ApJ...798L..21T 2015ApJ...798L..21T), assuming the distance inferred
in Section 3.
Note (5): Optical velocity, from the Hα emission lines reported in
Tollerud+ (2015ApJ...798L..21T 2015ApJ...798L..21T).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 F13.11 Mpc DistA [4.8/7.5] Distance, Pisces A
15- 27 F13.10 mag mu814A [24/25.3] F814W magnitude of the TRGB, Pisces A
29- 42 F14.12 mag ColTRGBA [0.7/0.9] (F606W-F814W)0 color of the TRGB,
Pisces A
44- 60 F17.15 --- alphaA [0.0008/0.9] TRGB model, power law slope for
the RGB component, Pisces A (1)
62- 75 F14.12 --- betaA [0.3/2] TRGB model, power-law slope for the
non-RGB population, Pisces A (1)
77- 90 F14.12 --- fA TRGB model, fraction of stars in the non-RGB
relative to those in the RGB, Pisces A (1)
92-104 F13.10 mag F606WA [17.3/17.4] HST ACS/WFC F606W, Pisces A
106-118 F13.10 mag F814WA [16.5/16.7] HST ACS/WFC F814W, Pisces A
120-133 F14.12 --- nA [0.42/0.54] Sersic Index, Pisces A
135-148 F14.12 --- ellA [0.29/0.4] Ellipticity in F606W, Pisces A
150-162 F13.9 deg PAA [131/142] Position angle, Pisces A
164-176 F13.11 arcsec ReffA [8.7/9.5] on-sky half-light radius in F606W,
Pisces A
178-190 F13.9 pc reffA [118/194] Physical half-light radius in F606W,
Pisces A
192-205 F14.11 Mpc DistB [6.7/12.3] Distance, Pisces B
207-219 F13.10 mag mu814B [25/26.4] F814W magnitude of the TRGB, Pisces B
221-234 F14.12 mag ColTRGBB [0.8/0.91] (F606W-F814W)0 color of the TRGB,
Pisces B
236-252 F17.15 --- alphaB [0/1.3] TRGB model, power law slope for the RGB
component, Pisces B (1)
254-266 F13.11 --- betaB [1/5] TRGB model, power-law slope for the
non-RGB population, Pisces B (1)
268-281 F14.12 --- fB TRGB model, fraction of stars in the non-RGB
relative to those in the RGB, Pisces B (1)
283-295 F13.10 mag F606WB [16.9/17] HST ACS/WFC F606W, Pisces B
297-309 F13.10 mag F814WB [16.4/16.5] HST ACS/WFC F814W, Pisces B
311-324 F14.12 --- nB [0.63/0.66] Sersic Index, Pisces B
326-339 F14.12 --- ellB [0.51/0.53] Ellipticity in F606W, Pisces B
341-353 F13.9 deg PAB [138/140] Position angle, Pisces B
355-367 F13.10 arcsec ReffB [10.2/10.6] on-sky half-light radius in F606W,
Pisces B
369-381 F13.9 pc reffB [242/446] Physical half-light radius in F606,
Pisces B
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Note (1): Parameters of the TRGB model in equation 1 of the text.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 24-Nov-2016