J/ApJ/805/99 Ages of star clusters in tidal tails of 3 galaxies (Mulia+, 2015)
Ages of star clusters in the tidal tails of merging galaxies.
Mulia A.J., Chandar R., Whitmore B.C.
<Astrophys. J., 805, 99 (2015)>
=2015ApJ...805...99M 2015ApJ...805...99M
ADC_Keywords: Clusters, globular ; Galaxies, nearby ; Photometry, HST
Keywords: galaxies: interactions; galaxies: star clusters: general ;
galaxies: star clusters: individual: (NGC 520, NGC 2623, NGC 3256);
galaxies: star formation
Abstract:
We study the stellar content in the tidal tails of three nearby
merging galaxies, NGC 520, NGC 2623, and NGC 3256, using BVI imaging
taken with the Advanced Camera for Surveys on board the Hubble Space
Telescope (HST). The tidal tails in all three systems contain compact
and fairly massive young star clusters, embedded in a sea of diffuse,
unresolved stellar light. We compare the measured colors and
luminosities with predictions from population synthesis models to
estimate cluster ages and find that clusters began forming in tidal
tails during or shortly after the formation of the tails themselves.
We find a lack of very young clusters (≤10Myr old), implying that
eventually star formation shuts off in the tails as the gas is used up
or dispersed. There are a few clusters in each tail with estimated
ages that are older than the modeled tails themselves, suggesting that
these may have been stripped out from the original galaxy disks. The
luminosity function of the tail clusters can be described by a single
power-law, dN/dL∝Lα, with -2.6<α←2.0. We find a
stellar age gradient across some of the tidal tails, which we
interpret as a superposition of (1) newly formed stars and clusters
along the dense center of the tail and (2) a sea of broadly
distributed, older stellar material ejected from the progenitor
galaxies.
Description:
Observations of NGC 520 and NGC 2623 were taken with the WFC on the
ACS on HST as part of program GO-9735 (PI: Whitmore). NGC 520 was
observed in 2004 October using the filters F435W (∼B in the
Johnson-Cousins system; exposed for 2400s), F555W (∼V; 1000s), and
F814W (∼I; 1200s). Observations of NGC 2623 were taken in 2004
February using the same filters with exposure times of 3730, 1206, and
2460s, respectively. Images of NGC 3256 come from two separate
observing proposals. F555W filter observations of NGC 3256 were
obtained in 2003 November as part of the program GO-9735 (2552s). WFC
observations using F435W and F814W filters were taken in 2005 November
as part of program GO-10592 (PI: Evans) for 1320 and 760s,
respectively. See figure 2 for the galaxy components.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 76 6 Properties of star clusters
table4.dat 73 411 Cluster catalog
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/MNRAS/405/857 : Star clusters in NGC 3256 (Goddard+, 2010)
J/A+A/435/65 : UBVI phot. of NGC 6872 clusters population (Bastian+, 2005)
J/A+AS/139/393 : Young Massive Star Clusters. II. (Larsen, 1999)
J/AJ/118/752 : BI phot. of NGC 3256 young globular clusters (Zepf+, 1999)
J/AJ/109/960 : Young star clusters in The Antennae (Whitmore+ 1995)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [NGC]
5- 8 I4 --- NGC Galaxy NGC number
9 A1 --- m_NGC [NSEP] Tidal tail identifier
10- 18 A9 --- n_NGC Tidal tail detailed name
20- 21 A2 --- l_tauT [≤ ] Limit flag on tau
22- 24 I3 Myr tauT [220/450] Predicted age of the tidal tail as
estimated from simulations (τtail)
26- 28 I3 --- Ncl [5/141] Total number of clusters found in
the region
30- 33 F4.2 kpc-2 Cl [0/8.5] star cluster density per kpc2 where
MV←8.5 (Σclus)
35- 36 A2 --- l_tauC [≥∼ ] Limit flag on tauC
37- 39 I3 Myr tauC [100/260]? Approximate age of the bulk cluster
formation (τclus)
41- 44 F4.2 mag <B-V> [0.05/0.3] B-V color index (1)
46- 49 F4.2 mag e_<B-V> [0.05/0.2] <B-V> uncertainty
51- 54 F4.2 mag <V-I> [0.3/0.6] V-I color index (1)
56- 59 F4.2 mag e_<V-I> [0.05/0.3] <V-I> uncertainty
61- 65 F5.2 --- alpha [-2.7/-2]? Luminosity function α value (2)
67- 70 F4.2 --- e_alpha [0.2/0.4]? alpha uncertainty
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Note (1): Median colors (<B-V>, <V-I>) are for clusters younger than the
age of the tidal tail.
Note (2): The luminosity function of the tail clusters is described by a
power-law function dN/dL∝Lα. The value of α was
derived using a fixed number of clusters per bin αconst-num
(the alternative is using a fixed magnitude bin width αconst-mag)
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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- 4 I4 --- NGC Galaxy NGC number
5 A1 --- m_NGC [NSEP] Tidal tail identifier
7- 9 I3 --- Seq [1/141] Cluster identifier in galaxy tidal tail
11- 12 I2 h RAh Hour of Right Ascension (J2000)
14- 15 I2 min RAm Minute of Right Ascension (J2000)
17- 21 F5.2 s RAs Second of Right Ascension (J2000)
23 A1 --- DE- Sign of the Declination (J2000)
24- 25 I2 deg DEd Degrees of Declination (J2000)
27- 28 I2 arcmin DEm Arc minute of Declination (J2000)
30- 34 F5.2 arcsec DEs Arc second of Declination (J2000)
36- 40 F5.2 mag Bmag [21.5/27.2] Apparent HST/ACS B band magnitude
42- 45 F4.2 mag e_Bmag [0/0.4] Error in Bmag
47- 51 F5.2 mag Vmag [21.4/26.4] Apparent HST/ACS V band magnitude
53- 56 F4.2 mag e_Vmag [0.01/0.3] Error in Vmag
58- 62 F5.2 mag Imag [20.9/26.6] Apparent HST/ACS I band magnitude
64- 67 F4.2 mag e_Imag [0/0.6] Error in Imag
69- 73 F5.2 [yr] logAge [5.1/10.3] Cluster age
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Emmanuelle Perret [CDS] 14-Sep-2015