Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCircumnuclear Regions of Star Formation in Early Type Galaxies
111
0
0.0
(
0
)
Authors
Angeles I. Diaz
Ask ChatGPT about the research
No Arabic abstract
Circumnuclear star forming regions, also called hotspots, are often found in the inner regions of some spiral galaxies where intense processes of star formation are taking place. In the UV, massive stars dominate the observed circumnuclear emission even in the presence of an active nucleus, contributing between 30 and 50% to the H$beta$ total emission of the nuclear zone. Spectrophotometric data of moderate resolution (3000 < R < 11000) are presented from which the physical properties of the ionized gas: electron density, oxygen abundances, ionization structure etc. have been derived.
rate research
Read More
We present the measurements of gas and stellar velocity dispersions in 17 circumnuclear star-forming regions (CNSFRs) and the nuclei of three barred spiral galaxies: NGC2903, NGC3310 and NGC3351 from high dispersion spectra. The stellar dispersions have been obtained from the CaII triplet (CaT) lines at 8494, 8542, 8662A, while the gas velocity dispersions have been measured by Gaussian fits to the Hbeta and to the [OIII]5007A lines. The CNSFRs, with sizes of about 100 to 150pc in diameter, are seen to be composed of several individual star clusters with sizes between 1.5 and 6.2pc on HST images. Using the stellar velocity dispersions, we have derived dynamical masses for the entire star-forming complexes and for the individual star clusters. Values of the stellar velocity dispersions are between 31 and 73 km/s. Dynamical masses for the whole CNSFRs are between 4.9x10^6 and 1.9x10^8 Mo and between 1.4x10^6 and 1.1x10^7 Mo for the individual star clusters. We have found indications for the presence of two different kinematical components in the ionized gas of the regions. The narrow component of the two-component Gaussian fits seem to have a relatively constant value for all the studied CNSFRs, with estimated values close to 25 km/s. This narrow component could be identified with ionized gas in a rotating disc, while the stars and the fraction of the gas (responsible for the broad component) related to the star-forming regions would be mostly supported by dynamical pressure.
(Abbr.) A study of cicumnuclear star-forming regions (CNSFRs) in several early type spirals has been made in order to investigate their main properties: stellar and gas kinematics, dynamical masses, ionising stellar masses, chemical abundances and other properties of the ionised gas. Both high resolution (R$ sim $20000) and moderate resolution (R ~ 5000) have been used. In some cases these regions, about 100 to 150 pc in size, are seen to be composed of several individual star clusters with sizes between 1.5 and 4.9 pc estimated from Hubble Space Telescope (HST) images. Stellar and gas velocity dispersions are found to differ by about 20 to 30 km/s with the H$beta$ emission lines being narrower than both the stellar lines and the [OIII] $lambda$ 5007 AA lines. The twice ionized oxygen, on the other hand, shows velocity dispersions comparable to those shown by stars. We have applied the virial theorem to estimate dynamical masses of the clusters, assuming that systems are gravitationally bounded and spherically symmetric, and using previously measured sizes. The measured values of the stellar velocity dispersions yield dynamical masses of the order of 10$^7$ to 10$^8$ solar masses for the whole CNSFRs. ...
We have obtained long-slit observations in the optical and near infrared of 12 circumnuclear HII regions (CNSFR) in the early type spiral galaxies NGC 2903, NGC 3351 and NGC 3504 with the aim of deriving their chemical abundances. Only for one of the regions, the [SIII] $lambda$ 6312 AA was detected providing, together with the nebular [SIII] lines at $lambdalambda$ 9069, 9532 AA, a value of the electron temperature of T$_e$([SIII])= 8400$^{+ 4650}_{-1250}$K. A semi-empirical method for the derivation of abundances in the high metallicity regime is presented. We obtain abundances which are comparable to those found in high metallicity disc HII regions from direct measurements of electron temperatures and consistent with solar values within the errors. The region with the highest oxygen abundance is R3+R4 in NGC 3504, 12+log(O/H) = 8.85, about 1.5 solar if the solar oxygen abundance is set at the value derived by Asplund et al. (2005), 12+log(O/H)$_{odot}$ = 8.66$pm$0.05. Region R7 in NGC 3351 has the lowest oxygen abundance of the sample, about 0.6 times solar. In all the observed CNSFR the O/H abundance is dominated by the O$^+$/H$^+$ contribution, as is also the case for high metallicity disc HII regions. For our observed regions, however, also the S$^+$/S$^{2+}$ ratio is larger than one, contrary to what is found in high metallicity disc HII regions for which, in general, the sulphur abundances are dominated by S$^{2+}$/H$^+$...
Motivated by recent progress in the study of early-type galaxies owing to technological advances, the launch of new space telescopes and large ground-based surveys, we attempt a short review of our current understanding of the recent star-formation activity in such intriguing galactic systems.
We identify a total of 120 early-type Brightest Cluster Galaxies (BCGs) at 0.1<z<0.4 in two recent large cluster catalogues selected from the Sloan Digital Sky Survey (SDSS). They are selected with strong emission lines in their optical spectra, with both H{alpha} and [O II]{lambda}3727 line emission, which indicates significant ongoing star formation. They constitute about ~ 0.5% of the largest, optically-selected, low-redshift BCG sample, and the fraction is a strong function of cluster richness. Their star formation history can be well described by a recent minor and short starburst superimposed on an old stellar component, with the recent episode of star formation contributing on average only less than 1 percent of the total stellar mass. We show that the more massive star-forming BCGs in richer clusters tend to have higher star formation rate (SFR) and specific SFR (SFR per unit galaxy stellar mass). We also compare their statistical properties with a control sample selected from X-ray luminous clusters, and show that the fraction of star-forming BCGs in X-ray luminous clusters is almost one order of magnitude larger than that in optically-selected clusters. BCGs with star formation in cooling flow clusters usually have very flat optical spectra and show the most active star formation, which may be connected with cooling flows.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
