J/ApJ/931/121 CO emission in the Taffy galaxies. I. ALMA obs. (Appleton+, 2022)
The CO emission in the Taffy galaxies (UGC 12914/15) at 60pc resolution.
I. The battle for star formation in the turbulent Taffy bridge.
Appleton P.N., Emonts B., Lisenfeld U., Falgarone E., Guillard P.,
Boulanger F., Braine J., Ogle P., Struck C., Vollmer B., Yeager T.
<Astrophys. J., 931, 121 (2022)>
=2022ApJ...931..121A 2022ApJ...931..121A
ADC_Keywords: Galaxies, interacting; Carbon monoxide; Radial velocities;
Star Forming Region; Infrared sources; H II regions
Keywords: Interacting galaxies
Abstract:
We present Atacama Large Millimeter/submillimeter Array observations
at a spatial resolution of 0.2" (60pc) of CO emission from the Taffy
galaxies (UGC 12914/5). The observations are compared with narrowband
Paα, mid-IR, radio continuum and X-ray imaging, plus optical
spectroscopy. The galaxies have undergone a recent head-on collision,
creating a massive gaseous bridge that is known to be highly
turbulent. The bridge contains a complex web of narrow molecular
filaments and clumps. The majority of the filaments are devoid of star
formation, and fall significantly below the Kennicutt-Schmidt
relationship for normal galaxies, especially for the numerous regions
undetected in Paα emission. Within the loosely connected
filaments and clumps of gas we find regions of high velocity
dispersion that appear gravitationally unbound for a wide range of
likely values of XCO. Like the "Firecracker" region in the Antennae
system, they would require extremely high external dynamical or
thermal pressure to stop them dissipating rapidly on short crossing
timescales of 2-5Myr. We suggest that the clouds may be transient
structures within a highly turbulent multiphase medium that is
strongly suppressing star formation. Despite the overall turbulence in
the system, stars seem to have formed in compact hotspots within a
kiloparsec-sized extragalactic HII region, where the molecular gas has
a lower velocity dispersion than elsewhere, and shows evidence for a
collision with an ionized gas cloud. Like the shocked gas in the
Stephan's Quintet group, the conditions in the Taffy bridge shows how
difficult it is to form stars within a turbulent, multiphase, gas.
Description:
In the ALMA program 2016.1.01037.S, 37 full-sampled primary beam
pointings with the 12m array were made of the Taffy pair and bridge
in 12CO(2-1) (vrest=230.54GHz; see Figure 1(b)). See Section 2.1.
We use archival Hubble Space Telescope (HST) Near Infrared Camera and
Multi-Object Spectrometer (NICMOS) observations taken in the F187N and
F190N filters, which were centered on UGC 12915 from the archive.
These observations involved a small mosaic covering an area of
45.7x45.3arcsec2 centered on the galaxy. We subtracted the continuum
images to obtain a Paα image. See Section 2.2.
Deep observations were made as part of a radio polarization study of
the Taffy (project 19A-378) in the A-array of the VLA at 1.4GHz (L band)
and 6GHz (C band) during a 12.6hr period in 2019 August 10.
See Section 2.3.
We make use in this paper of a Chandra X-ray (0.5-8kev) point-source
image discussed in greater detail in Appleton+ (2015ApJ...812..118A 2015ApJ...812..118A),
and made available to us by those authors. The image was obtained in
2013. See Section 2.4.
We also make use of archival Spitzer observations in the IRAC and MIPS
bands. See Section 2.5.
Finally, observations of the Taffy System were made in moderate seeing
conditions (∼1"), and a 1" wide slit with the Double Beam Spectrograph
(DBSP) of the Palomar 5m telescope on 2021 January 9. See Section 2.6.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
00 01 38.32 +23 29 01.1 UGC 12914 = ZW III 125
00 01 41.93 +23 29 45.1 UGC 12915 = LEDA 129
----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 91 244 Properties of the extracted regions
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/AJ/109/960 : Young star clusters in The Antennae (Whitmore+ 1995)
J/AJ/126/1607 : IRAS Revised Bright Galaxy Sample (Sanders+, 2003)
J/ApJ/611/821 : A2125 in X-ray (Wang+, 2004)
J/ApJ/671/333 : Aperture photometry in NGC 5194 (Kennicutt+, 2007)
J/ApJ/714/1256 : Far-IR star formation rate indicators (Calzetti+, 2010)
J/AJ/140/75 : Antennae galaxies (NGC 4038/4039) revisited (Whitmore+, 2010)
J/A+A/550/A106 : Low-velocity shocks models (Lesaffre+, 2013)
J/ApJ/846/71 : M51 ISM structures from the CO maps of PAWS (Leroy+, 2017)
J/ApJ/872/16 : Star formation law revisited. I. (de los Reyes+, 2019)
J/A+A/647/A138 : Taffy system CO(1-0) datacube (Vollmer+, 2021)
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
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1- 3 A3 --- Reg Region identifier
5- 6 I2 h RAh [0] Hour of Right Ascension (J2000)
8- 9 I2 min RAm [1] Minute of Right Ascension (J2000)
11- 16 F6.3 s RAs [38.5/42] Second of Right
Ascension (J2000)
18 A1 --- DE- [+] Sign of Declination (J2000)
19- 20 I2 deg DEd [23] Degree of Declination (J2000)
22- 23 I2 arcmin DEm [29] Arcminute of Declination (J2000)
25- 28 F4.1 arcsec DEs [8/53] Arcsecond of Declination
(J2000)
30- 33 I4 km/s VsysCO [4154/4591]? Heliocentric radial
velocity, CO(2-1) (2)
35- 39 F5.1 km/s FWHM [25/146]? FWHM corrected for
instrumental resolution (2)
41- 42 I2 km/s e_FWHM [2/29]? Uncertainty in FWHM (2)
44- 47 F4.2 Jy.km/s SVdV [0.06/0.8]? Integrated flux of the
CO(2-1) profile, ΣSVΔV
49- 52 F4.2 Jy.km/s e_SVdV [0.01/0.1]? Uncertainty in SVdV
54- 56 F3.1 --- SQual [0/1] Quality factor of CO
spectrum (3)
58- 61 F4.2 [Msun/pc2] logMol [1.7/2.8]? Molecular surface
density (4)
63- 66 F4.2 [Msun/pc2] e_logMol [0.05/0.2]? Uncertainty in logMol
68 A1 --- f_logMol Flag on logMol (1)
70- 74 F5.2 10-16mW/m2/arcsec2 Paalpha [0.4/43]? Surface flux, Paα, in
10-16erg/s/cm2/arcsec2 (5)
75 A1 --- f_Paalpha Flag on Paalpha (1)
77- 80 F4.2 10-16mW/m2/arcsec2 e_Paalpha [0.2/1.2]? Uncertainty in Paalpha
82- 86 F5.2 [Msun/yr/kpc2] logSFR [-1.8/0.3]? Log of surface star
formation rate (5)
88 A1 --- f_logSFR Flag on logSFR (1)
90- 91 I2 --- fPaa [-1/1]? Paα detection flags (6)
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Note (1): Flag as follows:
a = Regions A1 to A4 have multiple CO components 1a, 1b, 2a, 2b, etc.
Their integrated Paα flux and SFR properties are combined.
Note (2): The best-fitting systemic heliocentric velocity (optical definition)
and FWHM, with uncertainties, of the CO profiles after fitting with a
Gaussian in km/s.
Note (3): Quality factor of CO spectrum. Only quality 1 are shown in the
figures as follows:
1.0 = good;
0.7 = weak detection;
0.5 = very weak;
0.4 = poor;
0.0 = undetected in CO line.
Note (4): Molecular surface density for nominal case of XCO=1/4XCO,20;
See the Appendix Section.
Note (5): Surface flux and star formation rates estimated from the
Paα emission assuming minimal (Case 1) extinction (see Sec. 5.1).
Note (6): Paα detection flags as follows:
0 = upper limit;
1 = a detection;
-1 = the region lies outside the Paα NICMOS coverage area.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 22-Mar-2024