ترغب بنشر مسار تعليمي؟ اضغط هنا

The Host Galaxies of Narrow-Line Seyfert 1s: Evidence for Bar-Driven Fueling

229   0   0.0 ( 0 )
 نشر من قبل D. Michael Crenshaw
 تاريخ النشر 2003
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We present a study of the host-galaxy morphologies of narrow- and broad-line Seyfert 1 galaxies (NLS1s and BLS1s) based on broad-band optical images from the Hubble Space Telescope archives. We find that large-scale stellar bars, starting at ~1 kpc from the nucleus, are much more common in NLS1s than BLS1s. Furthermore, the fraction of NLS1 spirals that have bars increases with decreasing full-width at half-maximum (FWHM) of the broad component of H-beta. These results suggest a link between the large-scale bars, which can support high fueling rates to the inner kpc, and the high mass-accretion rates associated with the supermassive black holes in NLS1s.


قيم البحث

اقرأ أيضاً

Two major challenges to unification schemes for active galactic nuclei (AGN) are the existence of Narrow-Line Seyfert 1s (NLS1s) and the existence of changing-look (CL) AGNs. AGNs can drastically change their spectral appearance in the optical (chang ing their Seyfert type) and/or in the X-ray region. We illustrate the CL phenomenon with our multi-wavelength monitoring of NGC 2617 and discuss its properties compared with NLS1s. There are few examples of CL NLS1s and the changes are mostly only in the X-ray region. It has been proposed that some of these could be cases of a tidal-disruption events (TDE) or supernova events. If BLRs have a flat geometry and NLS1s are seen face-on then we have to see CL cases only if the orientation of the BLR changes as a result of a TDE or a close encounter of a star without a TDE. If NLS1s include both high Eddington accretion rate and low-inclination AGNs then a significant fraction of NLS1s could be obscured and would not be identified as NLS1s. CL cases might happen more in such objects if dust sublimation occurs following a strong increase in the optical luminosity.
We present optical images of nearby 50 narrow-line Seyfert 1 galaxies (NLS1s) which cover all the NLS1s at z<0.0666 and $delta ge -25^{circ}$ known at the time of 2001. Among the 50 NLS1s, 40 images are newly obtained by our observations and 10 image s are taken from archive data. Motivated by the hypothesis that NLS1s are in an early phase of a super-massive black hole (BH) evolution, we present a study of NLS1 host galaxy morphology to examine trigger mechanism(s) of active galactic nuclei (AGNs) by seeing the early phase of AGN. With these images, we made morphological classification by eye inspection and by quantitative method, and found a high bar frequency of the NLS1s in the optical band; the bar frequency is $85 pm 7% among disk galaxies ($64- 71$% in total sample) which is more frequent than that (40-70%) of broad-line Seyfert 1 galaxies (BLS1s) and normal disk galaxies, though the significance is marginal. Our results confirm the claim by Crenshaw et al. (2003) with a similar analysis for 19 NLS1s. The frequency is comparable to that of HII/starburst galaxies. We also examined the bar frequency against width of the broad H$beta$ emission line, Eddington ratio, and black hole mass, but no clear trend is seen. Possible implications such as an evolutionary sequence from NLS1s to BLS1 are discussed briefly.
We present optical integral field spectroscopy for five $z<0.062$ narrow-line Seyfert 1 galaxies (NLS1s) host galaxies, probing their host galaxies at $gtrsim 2-3$ kpc scales. Emission lines in the nuclear AGN spectra and the large-scale host galaxy are analyzed separately, based on an AGN-host decomposition technique. The host galaxy gas kinematics indicates large-scale gas rotation in all five sources. At the probed scales of $gtrsim 2-3$ kpc, the host galaxy gas is found to be predominantly ionized by star formation without any evidence of a strong AGN contribution. None of the five objects shows specific star formation rates exceeding the main sequence of low-redshift star forming galaxies. The specific star formation rates for MCG-05-01-013 and WPVS 007 are roughly consistent with the main sequence, while ESO 399-IG20, MS 22549-3712, and TON S180 show lower specific star formation rates, intermediate to the main sequence and red quiescent galaxies. The host galaxy metallicities, derived for the two sources with sufficient data quality (ESO 399-IG20 and MCG-05-01-013), indicate central oxygen abundances just below the low-redshift mass-metallicity relation. Based on this initial case study, we outline a comparison of AGN and host galaxy parameters as a starting point for future extended NLS1 studies with similar methods.
Narrow-line Seyfert 1 galaxies (NLS1s) are active galactic nuclei (AGN) recently identified as a new class of $gamma$-ray sources. The high energy emission is explained by the presence of a relativistic jet observed at small angles, just like in the case of blazars. When the latter are observed at larger angles they appear as radio-galaxies, but an analogue parent population for beamed NLS1s has not yet been determined. In this work we analyze this problem by studying the physical properties of three different samples of parent sources candidates: steep-spectrum radio-loud NLS1s, radio-quiet NLS1s, and disk-hosted radio-galaxies, along with compact steep-spectrum sources. In our approach, we first derived black hole mass and Eddington ratio from the optical spectra, then we investigated the interaction between the jet and the narrow-line region from the [O III] $lambdalambda$4959,5007 lines. Finally, the radio luminosity function allowed us to compare their jet luminosity and hence determine the relations between the samples.
This work studies the optical emission line properties and physical conditions of the narrow line region (NLR) of seven narrow-line Seyfert 1 galaxies (NLS1). Our results show that the flux carried out by the narrow component of H-beta is, on average , 50% of the total line flux. As a result, the [OIII] 5007/H-beta ratio emitted in the NLR varies from 1 to 5, instead of the universally adopted value of 10. This has strong implications for the required spectral energy distribution that ionizes the NLR gas. Photoionization models that consider a NLR composed of a combination of matter-bounded and ionization-bounded clouds are successful at explaining the low [OIII] 5007/H-beta ratio and the weakness of low-ionization lines of NLS1s. Variation of the relative proportion of these two type of clouds nicely reproduce the dispersion of narrow line ratios found among the NLS1 sample. Assuming similar physical model parameters of both NLS1s and the normal Seyfert 1 galaxy NGC 5548, we show that the observed differences of emission line ratios between these two groups can be explained in terms of the shape of the input ionizing continuum. Narrow emission line ratios of NLS1s are better reproduced by a steep power-law continuum in the EUV -- soft X-ray region, with spectral index alpha ~ -2. Flatter spectral indices (alpha ~ -1.5) match the observed line ratios of NGC 5548 but are unable to provide a good match to the NLS1 ratios. This result is consistent with ROSAT observations of NLS1s, which show that these objects are characterized by steeper power-law indices than those of Sy1 galaxies with strong broad optical lines.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا