Star Formation Law at Sub-kpc Scale in the Elliptical Galaxy Centaurus A as Seen by ALMA

We present an extensive analysis of the relationship between star formation rate surface density () and molecular gas surface density () at sub-kpc scale in the elliptical galaxy Centaurus A (also known as NGC 5128) at the distance 3.8 Mpc. 12CO ( = 2-1) data from Atacama Large Millimetre/Sub-Millimetre Array SV data with very high resolution (2.9′′, 0.84′′), as well as 24 μm data from the Spitzer Space Telescope, were used. This is one of the first studies of the SF law on Centaurus A at this very high spatial resolution. The results showed a breakdown in star formation law with a index relating and at 185 pc. A significant correlation exists between surface densities of molecular gas and SFR with very long depletion time (68 Gy). In addition we examined the spatially resolved relationship between velocity dispersion and star formation rate surface density for the outer disk of this galaxy and we found that the average velocity dispersion is equal to 11.78 km/s. The velocity dispersion of the molecular ISM for the outer disk is found to follow a power relation with the star formation rate surface density , where β is the slope from the ordinary least square fitting. The value of β is about and is the power law index of the star formation law.

[1]  R. Kennicutt.  The Star Formation Law in Galactic Disks , 1989 .

[2]  I. Heywood,et al.  Star formation efficiency along the radio jet in Centaurus A , 2015, 1511.04310.

[3]  Edinburgh,et al.  THE PROPERTIES OF THE STAR-FORMING INTERSTELLAR MEDIUM AT z = 0.8–2.2 FROM HiZELS: STAR FORMATION AND CLUMP SCALING LAWS IN GAS-RICH, TURBULENT DISKS , 2012, 1209.1396.

[4]  P. Barmby,et al.  Star formation laws in the Andromeda galaxy: gas, stars, metals and the surface density of star formation , 2015, 1512.06675.

[5]  K. Taylor,et al.  The structure and kinematics of the ionized gas within NGC 5128 (Cen A) – I. TAURUS observations , 1987 .

[6]  R. Leighton,et al.  CO emission from Centaurus A , 1987 .

[7]  A. E. Wright,et al.  THEORY OF STAR FORMATION. , 1970 .

[8]  Santiago,et al.  INTERFEROMETRIC CO(3–2) OBSERVATIONS TOWARD THE CENTRAL REGION OF NGC 1068 , 2011, 1112.0108.

[9]  T. Phillips,et al.  CO J=1-0, 2-1 and 3-2 absorption and emission toward the nucleus of Centaurus A : probing the circumnuclear disk , 1991 .

[10]  France.,et al.  First detection of molecular gas in the shells of CenA , 2000, astro-ph/0003175.

[11]  Z. A. Ibrahim,et al.  Kennicutt-Schmidt Law in the Central Region of NGC 4321 as Seen by ALMA , 2016, Scientific Reports.

[12]  Antony A. Stark,et al.  Kinematics of molecular clouds. II. New data on nearby giant molecular clouds , 1989 .

[13]  E. Phinney,et al.  The kinematics of the molecular gas in Centaurus A , 1992 .

[14]  STAR FORMATION IN GALAXIES ALONG THE HUBBLE SEQUENCE , 1998, astro-ph/9807187.

[15]  K. Schawinski,et al.  UV-Optical Colors as Probes of Early-Type Galaxy Evolution , 2006, astro-ph/0601029.

[16]  E. Brinks,et al.  HERACLES: THE HERA CO LINE EXTRAGALACTIC SURVEY , 2009, 0905.4742.

[17]  E. Rosolowsky,et al.  The Role of Pressure in GMC Formation II: The H2-Pressure Relation , 2006, astro-ph/0605035.

[18]  D. Elbaz,et al.  Herschel observations of Cen A: stellar heating of two extragalactic dust clouds , 2011, 1109.5706.

[19]  G. Helou.  The IRAS Colors of Normal Galaxies , 1986 .

[20]  R. Teyssier,et al.  The ATLAS3D project - XXII. Low-efficiency star formation in early-type galaxies: hydrodynamic models and observations , 2012, 1212.2288.

[21]  K. Alatalo,et al.  The ATLAS3D Project – XXVIII. Dynamically driven star formation suppression in early-type galaxies , 2014, 1403.4850.

[22]  Formation of gas discs in merging galaxies , 2002, astro-ph/0201250.

[23]  B. Madore,et al.  THE STAR FORMATION LAW IN NEARBY GALAXIES ON SUB-KPC SCALES , 2008, 0810.2541.

[24]  H. Rix,et al.  MOLECULAR GAS AND STAR FORMATION IN NEARBY DISK GALAXIES , 2013, 1301.2328.

[25]  Canada.,et al.  How old are the stars in the halo of NGC 5128 (Centaurus A) , 2010, 1011.4309.

[26]  K. Alatalo,et al.  The ATLAS3D project – IV. The molecular gas content of early-type galaxies , 2011, 1102.4633.

[27]  K. Alatalo,et al.  The ATLAS3D project – XI. Dense molecular gas properties of CO-luminous early-type galaxies , 2011, 1112.3641.

[28]  S. Maddox,et al.  Molecular and atomic gas in dust lane early-type galaxies - I. Low star formation efficiencies in minor merger remnants , 2015, 1503.05162.

[29]  J. Einasto.  The Rate of Star Formation , 1972 .

[30]  A. Hirota,et al.  BREAKDOWN OF KENNICUTT–SCHMIDT LAW AT GIANT MOLECULAR CLOUD SCALES IN M33 , 2010, 1006.5764.

[31]  I. Karachentsev.  The Local Group and Other Neighboring Galaxy Groups , 2005 .

[32]  Chen Cao,et al.  PAH and Mid-Infrared Luminosities as Measures of Star Formation Rate in Spitzer First Look Survey Galaxies , 2005, astro-ph/0509281.

[33]  D. Calzetti,et al.  STAR FORMATION LAWS: THE EFFECTS OF GAS CLOUD SAMPLING , 2012, 1204.5659.

[34]  A. Eckart.  CO isotopic emission and the far-infrared continuum of Centaurus A. , 1989 .

[35]  E. Brinks,et al.  A CONSTANT MOLECULAR GAS DEPLETION TIME IN NEARBY DISK GALAXIES , 2011, 1102.1720.

[36]  A. Weiss,et al.  Molecular gas in NGC 6946 , 2002, astro-ph/0204072.

[37]  S. Madden,et al.  MIPS 24–160 μm photometry for the Herschel-SPIRE Local Galaxies Guaranteed Time Programs , 2012, 1202.4629.

[38]  J. Black,et al.  H2 emission and CO absorption in Centaurus A : Evidence for a circumnuclear molecular disk , 1990 .

[39]  Jun Jugaku,et al.  Star Forming Regions , 1987 .

[40]  Galaxy evolution explorer ultraviolet color-magnitude relations and evidence of recent star formation in early-type galaxies , 2004, astro-ph/0411327.

[41]  F. P. Israel.  Centaurus A – NGC 5128 , 1998 .

[42]  D. Iono,et al.  DISENTANGLING THE CIRCUMNUCLEAR ENVIRONS OF CENTAURUS A. I. HIGH-RESOLUTION MOLECULAR GAS IMAGING , 2009, 0901.1656.

[43]  S. Hamer,et al.  Atomic-to-molecular gas phase transition triggered by the radio jet in Centaurus A , 2016, 1605.05986.

[44]  F. Walter,et al.  DISCOVERY OF NUCLEAR WATER MASER EMISSION IN CENTAURUS A , 2013, 1305.6662.

[45]  N. Scoville,et al.  The properties of individual giant molecular clouds in M33 , 1990 .

[46]  A. Dekel,et al.  Survival of star-forming giant clumps in high-redshift galaxies , 2010, 1001.0765.

[47]  R. Morganti,et al.  The missing link: Tracing molecular gas in the outer filament of Centaurus A , 2016, 1605.06598.

[48]  D. Leisawitz.  Physical Properties of the Molecular Clouds Found in a CO Survey of Regions Around 34 Open Clusters , 1989 .

[49]  Jr.,et al.  The Global Schmidt law in star forming galaxies , 1997, astro-ph/9712213.

[50]  P. T. de Zeeuw,et al.  The Central Parsecs of Centaurus A: High-excitation Gas, a Molecular Disk, and the Mass of the Black Hole , 2007, 0709.1877.

[51]  S. Serjeant,et al.  The JCMT nearby galaxies legacy survey - IV. Velocity dispersions in the molecular interstellar medium in spiral galaxies , 2010, 1009.3279.

[52]  Spitzer Science Center,et al.  THE RELATIONSHIP BETWEEN MOLECULAR GAS AND STAR FORMATION IN LOW-MASS E/S0 GALAXIES , 2010, 1011.1497.

[53]  J. M. Jackson,et al.  Molecular absorption lines toward the nucleus of Centaurus A , 1990 .

[54]  W. Harris,et al.  The Distance to NGC 5128 (Centaurus A) , 2009, Publications of the Astronomical Society of Australia.

[55]  K. Alatalo,et al.  The ATLAS 3 D project – IV . The molecular gas content of early-type galaxies , 2010 .

[56]  N. Evans,et al.  Star Formation in the Milky Way and Nearby Galaxies , 2012, 1204.3552.

[57]  Neutral hydrogen in nearby elliptical and lenticular galaxies: the continuing formation of early-type galaxies , 2006, astro-ph/0606261.