اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدDust and star formation in the centre of NGC 3311
82
0
0.0
(
0
)
تأليف
T. Richtler
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
NGC 3311 is the central galaxy of the Hydra I galaxy cluster. It has a hot interstellar medium and hosts a central dust lane with emission lines. These dust lanes are frequent in elliptical galaxies, but the case of NGC 3311 might be particularly interesting for problems of dust lifetime and the role of cool gas in the central parts. We aim to use archival HST images and MUSE data to investigate the central dust structure of NGC 3311. We used the tool PyParadise to model the stellar population and extract the emission lines. The HST/ACS colour map reveals the known dust structures, but also blue spots, which are places of strong line emission. A dusty mini-jet emanates from the centre. The distribution of the emission line gas matches the dust silhouette almost exactly. Close to the brightest Halpha emission, the ratio [NII]/Halpha resembles that of HII-regions; in the outer parts, [NII] gets stronger and is similar to LINER-like spectra. The gas kinematics is consistent with that of a rotating disc. The Doppler shifts of the strongest line emissions, which indicate the areas of highest star formation activity, smoothly fit into the disc symmetry. The metallicity is supersolar. The presence of neutral gas is indicated by the fit residuals of the stellar NaI D absorption line, which we interpret as interstellar absorption. We estimate the mass of the neutral gas to be of the order of the X-ray mass. The dynamical mass infers a stellar population of intermediate age, whose globular clusters have already been identified. Our findings can be harmonised in a scenario in which the star formation is triggered by the accretion of cold gas onto a pre-existing gas/dust disc or ring. Newly produced dust then contributes to the longevity of the dust.
قيم البحث
اقرأ أيضاً
NGC 1808 is a nearby barred spiral galaxy which hosts young stellar clusters in a patchy circumnuclear ring with a radius of $sim 240,mathrm{pc}$. In order to study the gaseous and stellar kinematics and the star formation properties of the clusters,
we perform seeing-limited $H+K$-band near-infrared integral-field spectroscopy with SINFONI of the inner $sim 600,mathrm{pc}$. From the $M_mathrm{BH}-sigma_*$ relation, we find a black hole mass of a few $10^7,M_odot$. We estimate the age of the young stellar clusters in the circumnuclear ring to be $lesssim 10,mathrm{Myr}$. No age gradient along the ring is visible. However, the starburst age is comparable to the travel time along the ring, indicating that the clusters almost completed a full orbit along the ring during their life time. In the central $sim 600,mathrm{pc}$, we find a hot molecular gas mass of $sim 730,M_odot$ which, with standard conversion factors, corresponds to a large cold molecular gas reservoir of several $10^8,M_odot$, in accordance with CO measurements from the literature. The gaseous and stellar kinematics show several deviations from pure disc motion, including a circumnuclear disc and signs of a nuclear bar potential. In addition, we confirm streaming motions on $sim 200,mathrm{pc}$ scale that have recently been detected in CO(1-0) emission. Due to our enhanced angular resolution of $<1,mathrm{arcsec}$, we find further streaming motion within the inner arcsecond, that have not been detected until now. Despite the flow of gas towards the centre, no signs for significant AGN activity are found. This raises the questions what determines whether the infalling gas will fuel an AGN or star formation.
The inner few hundred parsecs of the Milky Way harbours gas densities, pressures, velocity dispersions, an interstellar radiation field and a cosmic ray ionisation rate orders of magnitude higher than the disc; akin to the environment found in star-f
orming galaxies at high-redshift. Previous studies have shown that this region is forming stars at a rate per unit mass of dense gas which is at least an order of magnitude lower than in the disc, potentially violating theoretical predictions. We show that all observational star formation rate diagnostics - both direct counting of young stellar objects and integrated light measurements - are in agreement within a factor two, hence the low star formation rate is not the result of the systematic uncertainties that affect any one method. As these methods trace the star formation over different timescales, from $0.1 - 5$ Myr, we conclude that the star formation rate has been constant to within a factor of a few within this time period. We investigate the progression of star formation within gravitationally bound clouds on $sim$ parsec scales and find $1 - 4$ per cent of the cloud masses are converted into stars per free-fall time, consistent with a subset of the considered volumetric star formation models. However, discriminating between these models is obstructed by the current uncertainties on the input observables and, most importantly and urgently, by their dependence on ill-constrained free parameters. The lack of empirical constraints on these parameters therefore represents a key challenge in the further verification or falsification of current star formation theories.
The star formation rate in the Central Molecular Zone (CMZ) is an order of magnitude lower than predicted according to star formation relations that have been calibrated in the disc of our own and nearby galaxies. Understanding how and why star forma
tion appears to be different in this region is crucial if we are to understand the environmental dependence of the star formation process. Here, we present the detection of a sample of high-mass cores in the CMZs dust ridge that have been discovered with the Submillimeter Array as part of the CMZoom survey. These cores range in mass from ~ 50 - 2150 Msun within radii of 0.1 - 0.25 pc. All appear to be young (pre-UCHII), meaning that they are prime candidates for representing the initial conditions of high-mass stars and sub-clusters. We report that at least two of these cores (c1 and e1) contain young, high-mass protostars. We compare all of the detected cores with high-mass cores in the Galactic disc and find that they are broadly similar in terms of their masses and sizes, despite being subjected to external pressures that are several orders of magnitude greater - ~ 10^8 K/cm^3, as opposed to ~ 10^5 K/cm^3. The fact that > 80% of these cores do not show any signs of star-forming activity in such a high-pressure environment leads us to conclude that this is further evidence for an increased critical density threshold for star formation in the CMZ due to turbulence.
NGC1266 is a nearby lenticular galaxy that harbors a massive outflow of molecular gas powered by the mechanical energy of an active galactic nucleus (AGN). It has been speculated that such outflows hinder star formation (SF) in their host galaxies, p
roviding a form of feedback to the process of galaxy formation. Previous studies, however, indicated that only jets from extremely rare, high power quasars or radio galaxies could impart significant feedback on their hosts. Here we present detailed observations of the gas and dust continuum of NGC1266 at millimeter wavelengths. Our observations show that molecular gas is being driven out of the nuclear region at $dot{M}_{rm out} approx 110 M_odot$ yr$^{-1}$, of which the vast majority cannot escape the nucleus. Only 2 $M_odot$ yr$^{-1}$ is actually capable of escaping the galaxy. Most of the molecular gas that remains is very inefficient at forming stars. The far-infrared emission is dominated by an ultra-compact ($lesssim50$pc) source that could either be powered by an AGN or by an ultra-compact starburst. The ratio of the SF surface density ($Sigma_{rm SFR}$) to the gas surface density ($Sigma_{rm H_2}$) indicates that SF is suppressed by a factor of $approx 50$ compared to normal star-forming galaxies if all gas is forming stars, and $approx$150 for the outskirt (98%) dense molecular gas if the central region is is powered by an ultra-compact starburst. The AGN-driven bulk outflow could account for this extreme suppression by hindering the fragmentation and gravitational collapse necessary to form stars through a process of turbulent injection. This result suggests that even relatively common, low-power AGNs are able to alter the evolution of their host galaxies as their black holes grow onto the M-$sigma$ relation.
Early-type galaxies show a strong size evolution with redshift. This evolution is explained by fast in-situ star formation at high-$z$ followed by a late mass assembly mostly driven by minor mergers that deposit stars primarily in the outer halo. We
aim to identify structural components of the Hydra I cD galaxy NGC 3311 to investigate the connection between the central galaxy and the surrounding stellar halo. We map the line-of-sight velocity distribution (LOSVD) using MUSE pointings covering NGC 3311 out to $25$ kpc. Combining photometric and spectroscopic data, we model the LOSVD maps using a finite mixture distribution, including four non-concentric, nearly isothermal spheroids, with different line-of-sight systemic velocities $V$, velocity dispersions $sigma$, and higher order Gauss-Hermite moments $h_3$ and $h_4$. The comparison of the correlations between $h_3$ and $h_4$ with $V/sigma$ with simulations indicates that NGC 3311 assembled mainly through dry mergers. The $sigma$ profile rises to $simeq 400$ km s$^{text -1}$ at 20 kpc indicating that stars there were stripped from progenitors orbiting in the cluster core. The finite mixture distribution modeling supports three inner components related to the central galaxy and a fourth component with large effective radius ($51$ kpc) and velocity dispersion ($327$ km s$^{text{-1}}$) consistent with a cD envelope. We find that the cD envelope is offset from the center of NGC 3311 both spatially (8.6 kpc) and in velocity ($Delta V = 204$ kms$^{-1}$), but coincide with the cluster core X-ray isophotes and the mean velocity of galaxies. Also, the envelope contributes to the broad wings of the LOSVD measured by large $h_4$ within 10 kpc. The cD envelope of NGC 3311 is dynamically associated with the cluster core, which in Hydra I is in addition displaced from the cluster center, presumably due to a recent subcluster merger.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
