arXiv subjects

Eija Laurikainen

Publications and source records attributed to Eija Laurikainen.

39 records · Page 3Linked to original sources

arXiv2005

Multicomponent Decompositions for a Sample of S0 galaxies

We have estimated the bulge-to-total ($B/T$) light ratios in the $K_s$-band for a sample of 24 S0, S0/a and Sa galaxies by applying a 2-dimensional multicomponent decomposition method. For the disk an exponential function is used, the bulges are fitted by a Sérsic's $R^{1/n}$ function and the bars and ovals are described either by a Sérsic or a Ferrers function. In order to avoid non-physical solutions, preliminary characterization of the structural components is made by inspecting the radial profiles of the orientation parameters and the low azimuthal wavenumber Fourier amplitudes and phases. In order to identify also the inner structures, unsharp masks were created: previously undetected inner spiral arms were found in NGC 1415 and marginally in NGC 3941. Most importantly, we found that S0s have a mean $ _K$-ratio of 0.24 $\pm$ 0.11, which is significantly smaller than the mean $ _R$ = 0.6 generally reported in the literature. Also, the surface brightness profiles of the bulges in S0s were found to be more exponential-like than generally assumed, the mean shape parameter of the bulge being $ $ = 2.1 $\pm$ 0.7. We did not find examples of barred S0s lacking the disk component, but we found some galaxies (NGC 718, NGC 1452, NGC 4608) having a non-exponential disk in the bar region. To our knowledge our study is the first attempt to apply a multicomponent decomposition method for a moderately sized sample of early-type disk galaxies

astro-ph↗

arXiv2003

Galaxy interactions - poor starburst triggers

We report on a study of tidally triggered star formation in galaxies, based on spectroscopic/photometric observations in the optical/near-IR of a magnitude limited sample of 59 systems of interacting and merging galaxies and a comparison sample of 38 normal isolated galaxies. In contrast to results from previous investigations, our global UBV colours do not support a significant enhancement of starforming activity in the interacting/merging galaxies. We claim that this is true also for Arp galaxies. A moderate increase in star formation is found in the very centres of the interacting galaxies contributing marginally to the total luminosity. The interacting and in particular the merging galaxies are characterized by increased far infrared (hereafter FIR) luminosities and temperatures that weakly correlate with the central activity. The L(FIR)/L(B) ratio however, is remarkably similar in the two samples, indicating that true starbursts normally are not hiding in the central regions of the FIR luminous cases. The gas mass-to-luminosity ratio in optical-IR is practically independent of luminosity, lending further support to the paucity of true massive starburst galaxies triggered by interactions/mergers. Our conclusion is that interacting and merging galaxies, from the global star formation aspect, generally do not differ dramatically from scaled up versions of normal, isolated galaxies. No drastic change with redshift is expected.

astro-ph↗

arXiv2002

Bar strengths in spiral galaxies estimated from 2MASS images

Non-axisymmetric forces are presented for 107 spiral galaxies using the 2 Micron All Sky Survey (2MASS) images. We apply both Cartesian integration and a polar grid integration utilizing a limited number of azimuthal Fourier components of density. We found that bar strength is independent of the method used to evaluate the gravitational potential. However, the polar method is more suitable for weak and noisy images. Bar strength was found to be sensitive to the Hubble-type dependent scale height of the disk, which has been ignored in the previous studies. On the other hand, the method is rather insensitive to the vertical model of the disk, as long as a same vertical dispersion is assumed, or to the boxy/peanut shaped structure, studied in terms of non-constant vertical scale height along the disk. In the near-IR most galaxies in our sample show non-axisymmetric forces in some level, and 40 percent of them have bars in a sense that they have regions with a constant phase of the m=2 Fourier density component.

astro-ph↗