Parameters of the brightest star formation regions in the two principal spiral arms of NGC 628

Abstract

We study photometric properties, chemical abundances and sizes of star formation regions in the two principal arms of the galaxy NGC 628 (M74). The GALEX ultraviolet, optical U BVRI, and Hα surface photometry data are used, including those obtained with the 1.5-m telescope of the Maidanak Observatory. The thirty brightest star formation regions in ultraviolet light located in the spiral arms of NGC 628 are identified and studied. We find that the star formation regions in one (longer) arm are systematically brighter and larger than the regions in the other (shorter) arm. However, both luminosity and size distribution functions have approximately the same slopes for the samples of star formation regions in both arms. The star formation regions in the longer arm have a higher star formation rate density than the regions in the shorter arm. The regions in the shorter arm show higher N/O ratio at a higher oxygen abundance, but they have lower ultraviolet and Hα luminosities. These findings can be explained if we assume that star formation regions in the shorter arm had higher star formation rate in the past, but now it is lower than for those in the opposite arm. Results of stellar evolutionary synthesis show that the brightest regions in the longer arm are slightly younger than the ones in the shorter arm (3.5 ± 2.2 Myr versus 6.0 ± 1.1 Myr). Our results demonstrate that there is a difference in the inner structures and parameters of the interstellar medium between the spiral arms of NGC 628, one of which is long and hosts a regular chain of bright star formation complexes and the other, shorter one does not.

Metallicity and star formation activities of the interacting system Arp 86 from observations with MOS on the Xinglong 2.16 m telescope

“…The slope is one order of magnitude lower than the typical values of 0.03-0.10 dex kpc −1 in normal spiral galaxies, such as NGC 628 (Gusev et al, 2013), NGC 3621 (Bresolin et al, 2012), M33 (Bresolin, 2011), M101 (Lin et al, 2013). Their observational results provide similar evidences.…”

Star formation rates and the kinematics of gas in the spiral arms of NGC 628

“…Moreover, a significant contribution to the increase in SFR is made by one of the brightest star formation regions, No. A12 (Gusev et al 2014 Note that the maximal velocity of gas inflow into the spiral arms is apparently achieved at distances r ∼ 4.5 − 5.0 kpc, as can be seen from the velocity graph in Fig. 4.…”

“…where diameters of star formation regions, d, were obtained in Gusev et al (2014). Arm B is distorted at the galactocentric distances r > 3.2 kpc (Fig.…”

“…Gusev et al (2014) selected 30 star formation regions having a total magnitude corrected for interstellar absorption FUV 0 < 19.8 mag. Among regions fainter than 19.8 mag in the FUV, we found a large number of diffuse objects without strong Hα emission.…”

“…Positions of star formation regions (red crosses in circles) from the list of Gusev et al (2014) are indicated in the FUV image. Logarithmic spiral arms (thick red curves) and the boundary between two parts of the galaxy, around Arm A and Arm B (thin cyan curve) are shown in the Hα line image.…”