Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userNGC3801 caught in the act: A post-merger starforming early-type galaxy with AGN-jet feedback
103
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
In the current models of galaxy formation and evolution, AGN feedback is crucial to reproduce galaxy luminosity function, colour-magnitude relation and M-sigma relation. However, if AGN-feedback can indeed expel and heat up significant amount of cool molecular gas and consequently quench star formation, is yet to be demonstrated observationally. Only in four cases so far (Cen A, NGC 3801, NGC 6764 and Mrk 6), X-ray observations have found evidences of jet-driven shocks heating the ISM. We chose the least-explored galaxy, NGC 3801, and present the first ultraviolet imaging and stellar population analysisis of this galaxy from GALEX data. We find this merger-remnant early-type galaxy to have an intriguing spiral-wisp of young star forming regions (age ranging from 100--500 Myr). Taking clues from dust/PAH, HI and CO emission images we interpret NGC 3801 to have a kinamatically decoupled core or an extremely warped gas disk. From the HST data we also show evidence of ionised gas outflow similar to that observed in HI and molecular gas (CO) data, which may have caused the decline of star formation leading to the red optical colour of the galaxy. However, from these panchromatic data we interpret that the expanding shock shells from the young ($sim$2.4 million years) radio jets are yet to reach the outer gaseous regions of the galaxy. It seems, we observe this galaxy at a rare stage of its evolutionary sequence where post-merger star formation has already declined and new powerful jet feedback is about to affect the gaseous star forming outer disk within the next 10 Myr, to further transform it into a red-and-dead early-type galaxy.
rate research
Read More
Direct evidence of stellar material from galaxy disruption in the intra-cluster medium (ICM) relies on challenging observations of individual stars, planetary nebulae and diffuse optical light. Here we show that the ultra-compact dwarf galaxies (UCDs) we have discovered in the Fornax Cluster are a new and easy-to-measure probe of disruption in the ICM. We present spectroscopic observations supporting the hypothesis that the UCDs are the remnant nuclei of tidally ``threshed dwarf galaxies. Deep optical imaging of the cluster has revealed a 43-kpc long arc of tidal debris, flanking a nucleated dwarf elliptical (dE,N) cluster member. We may be witnessing galaxy threshing in action.
We employ cosmological hydrodynamical simulations to investigate the effects of AGN feedback on the formation of massive galaxies with present-day stellar masses of $M_{stel} = 8.8 times 10^{10} - 6.0 times 10^{11} M_{sun}$. Using smoothed particle hydrodynamics simulations with a pressure-entropy formulation that allows an improved treatment of contact discontinuities and fluid mixing, we run three sets of simulations of 20 halos with different AGN feedback models: (1) no feedback, (2) thermal feedback, and (3) mechanical and radiation feedback. We assume that seed black holes are present at early cosmic epochs at the centre of emerging dark matter halos and trace their mass growth via gas accretion and mergers with other black holes. Both feedback models successfully recover the observed M_BH - sigma relation and black hole-to-stellar mass ratio for simulated central early-type galaxies. The baryonic conversion efficiencies are reduced by a factor of two compared to models without any AGN feedback at all halo masses. However, massive galaxies simulated with thermal AGN feedback show a factor of ~10-100 higher X-ray luminosities than observed. The mechanical/radiation feedback model reproduces the observed correlation between X-ray luminosities and velocity dispersion, e.g. for galaxies with sigma = 200 km/s, the X-ray luminosity is reduced from $10^{42}$ erg/s to $10^{40}$ erg/s. It also efficiently suppresses late time star formation, reducing the specific star formation rate from $10^{-10.5}$ $yr^{-1}$ to $10^{-14}$ $yr^{-1}$ on average and resulting in quiescent galaxies since z=2, whereas the thermal feedback model shows higher late time in-situ star formation rates than observed.
We investigate radio-mode AGN activity among post-starburst galaxies from the Sloan Digital Sky Survey to determine whether AGN feedback may be responsible for the cessation of star formation. Based on radio morphology and radio-loudness from the FIRST and NVSS data, we separate objects with radio activity due to an AGN from ongoing residual star formation. Of 513 SDSS galaxies with strong A-star spectra, 12 objects have 21-cm flux density above 1 mJy. These galaxies do not show optical AGN emission lines. Considering that the lifetime of radio emission is much shorter than the typical time-scale of the spectroscopic features of post-starburst galaxies, we conclude that the radio-emitting AGN activity in these objects was triggered after the end of the recent starburst, and thus cannot be an important feedback process to explain the post-starburst phase. The radio luminosities show a positive correlation with total galaxy stellar mass, but not with the mass of recently formed stars. Thus the mechanical power of AGN feedback derived from the radio luminosity is related to old stellar populations dominating the stellar mass, which in turn are related to the masses of central supermassive black holes.
Post starburst E+A galaxies are thought to have experienced a significant starburst that was quenched abruptly. Their disturbed, bulge-dominated morphologies suggest that they are merger remnants. We present ESI/Keck observations of SDSS J132401.63+454620.6, a post starburst galaxy at redshift z = 0.125, with a starburst that started 400 Myr ago, and other properties, like star formation rate (SFR) consistent with what is measured in ultra luminous infrared galaxies (ULRIGs). The galaxy shows both zero velocity narrow lines, and blueshifted broader Balmer and forbidden emission lines (FWHM=1350 +- 240 km/s). The narrow component is consistent with LINER-like emission, and the broader component with Seyfert-like emission, both photoionized by an active galactic nucleus (AGN) whose properties we measure and model. The velocity dispersion of the broad component exceeds the escape velocity, and we estimate the mass outflow rate to be in the range 4-120 Mo/yr. This is the first reported case of AGN-driven outflows, traced by ionized gas, in post starburst E+A galaxies. We show, by ways of a simple model, that the observed AGN-driven winds can consistently evolve a ULIRG into the observed galaxy. Our findings reinforce the evolutionary scenario where the more massive ULIRGs are quenched by negative AGN feedback, evolve first to post starburst galaxies, and later become typical red and dead ellipticals.
One possible channel for the formation of dwarf galaxies involves birth in the tidal tails of interacting galaxies. We report the detection of a bright UV tidal tail and several young tidal dwarf galaxy candidates in the post-merger galaxy NGC 4922 in the Coma cluster. Based on a two-component population model (combining young and old stellar populations), we find that the light of tidal tail predominantly comes from young stars (a few Myr old). The Galaxy Evolution Explorer (GALEX) ultraviolet data played a critical role in the parameter (age and mass) estimation. Our stellar mass estimates of the tidal dwarf galaxy candidates are ~ 10^{6-7} M_sun, typical for dwarf galaxies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
