J/ApJ/812/158 Leo P RR Lyrae candidates & cumulative SFH (McQuinn+, 2015)
Leo P: an unquenched very low-mass galaxy.
McQuinn K.B.W., Skillman E.D., Dolphin A., Cannon J.M., Salzer J.J.,
Rhode K.L., Adams E.A.K., Berg D., Giovanelli R., Girardi L., Haynes M.P.
<Astrophys. J., 812, 158 (2015)>
=2015ApJ...812..158M 2015ApJ...812..158M (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, variable ; Photometry, HST
Keywords: galaxies: distances and redshifts; galaxies: dwarf;
galaxies: evolution; galaxies: photometry; galaxies: stellar content;
stars: variables: RR Lyrae
Abstract:
Leo P is a low-luminosity dwarf galaxy discovered through the blind HI
Arecibo Legacy Fast ALFA survey. The HI and follow-up optical
observations have shown that Leo P is a gas-rich dwarf galaxy with
active star formation, an underlying older population, and an
extremely low oxygen abundance. We have obtained optical imaging with
the Hubble Space Telescope to two magnitudes below the red clump in
order to study the evolution of Leo P. We refine the distance
measurement to Leo P to be 1.62±0.15Mpc, based on the luminosity of
the horizontal branch stars and 10 newly identified RR Lyrae
candidates. This places the galaxy at the edge of the Local Group,
∼0.4Mpc from Sextans B, the nearest galaxy in the NGC 3109 association
of dwarf galaxies of which Leo P is clearly a member. The star
responsible for ionizing the HII region is most likely an O7V or O8V
spectral type, with a stellar mass ≳25M☉. The presence of this
star provides observational evidence that massive stars at the upper
end of the initial mass function are capable of being formed at star
formation rates as low as ∼10-5M☉/yr. The best-fitting star
formation history (SFH) derived from the resolved stellar populations
of Leo P using the latest PARSEC models shows a relatively constant
star formation rate over the lifetime of the galaxy. The modeled
luminosity characteristics of Leo P at early times are consistent with
low-luminosity dSph Milky Way satellites, suggesting that Leo P is
what a low-mass dSph would look like if it evolved in isolation and
retained its gas. Despite the very low mass of Leo P, the imprint of
reionization on its SFHIs subtle at best, and consistent with being
totally negligible. The isolation of Leo P, and the total quenching of
star formation of Milky Way satellites of similar mass, implies that
the local environment dominates the quenching of the Milky Way
satellites.
Description:
HST observations of Leo P were obtained using the Advance Camera for
Surveys (ACS) instrument in the F475W (Sloan g) and F814W (I) filters
between 2014 April 23 and 26 (GO 13376; PI McQuinn).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 34 327 Photometry of RR Lyrae Candidates
table3.dat 71 10 Summary of RR Lyrae Candidates in Leo P
table5.dat 20 71 Cumulative star formation history (SFH) of Leo P
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See also:
J/ApJ/800/51 : DUSTiNGS II. Metal-poor dusty AGB stars (Boyer+, 2015)
J/AJ/147/13 : Disturbers of nearby giant galaxies (Karachentsev+, 2014)
J/AJ/146/145 : ALFALFA discovery of Leo P. IV. VI photom. (McQuinn+, 2013)
J/ApJS/208/9 : Intrinsic colors & temperatures of PMS stars (Pecaut+, 2013)
J/AJ/145/149 : ALFALFA discovery of Leo P. II. BVR photometry (Rhode+, 2013)
J/AJ/145/101 : Updated nearby galaxy catalog (Karachentsev+, 2013)
J/AJ/144/134 : LITTLE THINGS survey of nearby dwarf galaxies (Hunter+, 2012)
J/ApJ/756/108 : HST VI phot. of variable stars in Leo T (Clementini+, 2012)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/AJ/143/133 : Dwarf galaxies from the ALFALFA survey (Huang+, 2012)
J/AJ/142/170 : ALFALFA survey: α.40 HI source catalog (Haynes+, 2011)
J/ApJS/191/352 : Abundances in stars of MW dwarf satellites (Kirby+, 2010)
J/AJ/138/1037 : Star formation in Centaurus A Group dwarfs (Cote+ 2009)
J/MNRAS/380/281 : Faint galactic satellites spectrosc. survey (Martin+, 2007)
J/AJ/128/2170 : Hα imaging of irregular galaxies (Hunter+, 2004)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/10] Identification number of star
4- 15 F12.6 d MJD Modified Julian Date of photometric epoch
17- 22 F6.3 mag mag [25.4/27.7] Photometric magnitude in Filter
24- 28 F5.3 mag e_mag [0.05/0.3] Uncertainty in mag
30- 34 A5 --- Filt HST/ACS filter for photometric measurement
(F475W (g) or F814W (I))
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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 --- Seq [1/10] Identification number of star
4- 5 I2 h RAh [10] Hour of Right Ascension (J2000)
7- 8 I2 min RAm [21] Minute of Right Ascension (J2000)
10- 15 F6.3 s RAs [42.7/47.1] Second of Right Ascension (J2000)
17 A1 --- DE- [+] Sign of the Declination (J2000)
18- 19 I2 deg DEd [18] Degree of Declination (J2000)
21- 22 I2 arcmin DEm [3/6] Arcminute of Declination (J2000)
24- 28 F5.2 arcsec DEs Arcsecond of Declination (J2000)
30- 34 F5.2 mag F475Wmag [26.8/27] HST/ACS F475W (g) band mean
magnitude (1)
36- 39 F4.2 mag e_F475Wmag [0.06/0.2] Uncertainty in F475mag
41- 45 F5.2 mag F814Wmag [26/26.3] HST/ACS F814W (I) band mean
magnitude (1)
47- 50 F4.2 mag e_F814Wmag [0.05/0.07] Uncertainty in F814mag
52- 56 F5.2 mag Vmag [26.5/26.7] V band mean magnitude (1)
58- 61 F4.2 mag e_Vmag [0.09/0.2] Uncertainty in Vmag
63- 66 F4.2 d Per [0.3/0.7] Mean period
68- 71 F4.2 d e_Per [0.01/0.2] Uncertainty in Per
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Note (1): The mean magnitudes for all 10 candidates in Leo P for the F475W,
F814W and V bands are 26.88±0.02, 26.18±0.07 and
26.62±0.03, respectively.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 5 F5.2 [yr] logt [6.6/10.1] Log time
7- 10 F4.2 --- mass [0.1/1] Percent of mass formed prior to logt
12- 15 F4.2 --- E_mass [0/0.5] Upper uncertainty on mass
17- 20 F4.2 --- e_mass [0/0.3] Lower uncertainty on mass
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 09-Feb-2016