J/ApJS/174/337 Star formation in nuclear rings (Mazzuca+, 2008)
A connection between star formation in nuclear rings and their host galaxies. Mazzuca L.M., Knapen J.H., Veilleux S., Regan M.W. <Astrophys. J. Suppl. Ser., 174, 337-365 (2008)> =2008ApJS..174..337M
ADC_Keywords: Galaxies, ring ; Equivalent widths ; H II regions ; Photometry, H-alpha Keywords: galaxies: spiral - galaxies: structure - stars: formation Abstract: We present results from a photometric Hα survey of 22 nuclear rings, aiming to provide insight into their star formation properties, including age distribution, dynamical timescales, star formation rates, and galactic bar influence. We find a clear relationship between the position angles and ellipticities of the rings and those of their host galaxies, which indicates the rings are in the same plane as the disk and circular. We use population synthesis models to estimate ages of each Hα-emitting (HII) region, which range from 1 to 10Myr throughout the rings. We find that approximately half of the rings contain azimuthal age gradients that encompass at least 25% of the ring, although there is no apparent relationship between the presence or absence of age gradients and the morphology of the rings or their host galaxies. NGC 1343, NGC 1530, and NGC 4321 show clear bipolar age gradients, where the youngest HII regions are located near the two contact points of the bar and ring. We speculate in these cases that the gradients are related to an increased mass inflow rate and/or an overall higher gas density in the ring, which would allow for massive star formation to occur on short timescales, after which the galactic rotation would transport the HII regions around the ring as they age. Two-thirds of the barred galaxies show correlation between the locations of the youngest HII region(s) in the ring and the location of the contact points, which is consistent with predictions from numerical modeling. Description: The ring images presented here are part of a larger William Herschel Telescope (WHT) imaging survey (1999 and 2000) conducted to characterize the nuclear and circumnuclear morphology in nearby galaxies (Paper I, Knapen et al., 2006A&A...448..489K). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file galaxies.dat 142 20 Galaxy list tables.dat 37 399 NGC or IC HII regions detected associated with the ring (tables 4 to 23 of the paper)
See also: J/AJ/128/2170 : Hα imaging of irregular galaxies (Hunter+, 2004) Byte-by-byte Description of file: galaxies.dat
Bytes Format Units Label Explanations
1- 8 A8 --- NGC/IC Galaxy name 11- 12 I2 h RAh Right ascension (J2000) 14- 15 I2 min RAm Right ascension (J2000) 17- 20 F4.1 s RAs Right ascension (J2000) 22 A1 --- DE- Declination sign (J2000) 23- 24 I2 deg DEd Declination sign (J2000) 26- 27 I2 arcmin DEm Declination sign (J2000) 29- 30 I2 arcsec DEs Declination sign (J2000) 34- 35 I2 --- NHII Number of HII regions in the galaxy 37-142 A106 --- Remarks Notes on the HII reguions detected.
Byte-by-byte Description of file: tables.dat
Bytes Format Units Label Explanations
1- 8 A8 --- NGC/IC Galaxy name 10- 11 I2 --- [MKV2008] HII region number (1) 13- 17 F5.2 10-16W/m2 Flux Integrated flux (in 10-13erg/cm2/s) 19- 24 F6.2 10+32W Lum Luminosity (in 1037erg/s) 26- 30 I5 0.1nm EW Hα equivalent width (Å) 32- 35 F4.2 [0.1nm] logEW Logarithm of EW 37 I1 --- CorFlux [0/1] Flux correction (2)
Note (1): Since SExtractor detects all HII regions in the supplied image, extraneous HII regions as well as the nucleus were included in the identification process. These superfluous detections are not included in the tables but are instead noted in the captions (above) for completeness sake. Note (2): Flag as follows: 0 = In the cases where the I-band flux generated from SExtractor was not modified; 1 = I-band flux needed to be modified in order to compensate for unrealistic values (i.e., negative flux values or marginally positive flux values. See section 4.2.1).
Nomenclature note: HII Region are <[MKV2008] NGC NNNN NN> or <[MKV2008] IC 1438 NN> in Simbad. History: From electronic version of the journal References: Knapen et al. Paper I. 2006A&A...448..489K
(End) Emmanuelle Perret [CDS] 01-Oct-2009
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