scholarly journals A Sober Look at Bars in Galaxies

1996 ◽  
Vol 157 ◽  
pp. 560-568
Author(s):  
William C. Keel
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Nuclear Activity ◽  
Secular Evolution ◽  
Key Issues

AbstractI review some of the more notable observational aspects of bars in galaxies. Key issues include the overall occurrence of bars, secular evolution of bars and bulges, the differences in bar properties with Hubble type, the role of bars in star formation and nuclear activity, and the evidence for a bar at the center of the Milky Way. These lead to a “wish list” of future observations.

scholarly journals The role of external gas accretion on galaxy transformations, and evidence of such accretion

2012 ◽  
Vol 10 (H16) ◽  
pp. 366-366
Author(s):  
Françoise Combes
Keyword(s):  
Star Formation ◽  
Mass Relation ◽  
Galaxy Interactions ◽  
Radial Migration ◽  
Secular Evolution ◽  
Gas Accretion ◽  
Bulge Formation ◽  
Inside Out

AbstractContinuously accreting matter from cosmic filaments is one of the main way to assemble mass for galaxies (Keres et al.2005, Dekel et al.2009). This external accretion accelerates secular processes, and maintain star formation, but also bar and spiral formation (Bournaud & Combes 2002), and consequent radial migration. Secular evolution may alleviate the problem of too massive bulge formation in the standard LCDM hierarchical scenario. Inside out formation of galaxies may account for the evolution of the size-mass relation and evolution with redshift. I will show how gas accretion from the inter galactic medium can mimick perturbations due to galaxy interactions (cf Figure 1), and I will describe evidence of such accretion, through warps, polar rings or damped Lyman-α systems.

scholarly journals SDSS-IV MaNGA: the indispensable role of bars in enhancing the central star formation of low-z galaxies

2020 ◽  
Vol 499 (1) ◽  
pp. 1406-1423 ◽  
Author(s):  
Lin Lin ◽  
Cheng Li ◽  
Cheng Du ◽  
Enci Wang ◽  
Ting Xiao ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Local Environment ◽  
Central Star ◽  
Barred Galaxies ◽  
Secular Evolution ◽  
Integral Field Spectroscopy ◽  
Radial Profiles ◽  
Order Of Magnitude

ABSTRACT We analyse two-dimensional maps and radial profiles of EW(Hα), EW(HδA), and Dn(4000) of low-redshift galaxies using integral field spectroscopy from the MaNGA survey. Out of ≈1400 nearly face-on late-type galaxies with a redshift z < 0.05, we identify 121 “turnover” galaxies that each have a central upturn in EW(Hα), EW(HδA), and/or a central drop in Dn(4000), indicative of ongoing/recent star formation. The turnover features are found mostly in galaxies with a stellar mass above ∼1010 M⊙ and NUV – r colour less than ≈5. The majority of the turnover galaxies are barred, with a bar fraction of 89 ± 3 per cent. Furthermore, for barred galaxies, the radius of the central turnover region is found to tightly correlate with one-third of the bar length. Comparing the observed and the inward extrapolated star formation rate surface density, we estimate that the central SFR have been enhanced by an order of magnitude. Conversely, only half of the barred galaxies in our sample have a central turnover feature, implying that the presence of a bar is not sufficient to lead to a central SF enhancement. We further examined the SF enhancement in paired galaxies, as well as the local environment, finding no relation. This implies that the environment is not a driving factor for central SF enhancement in our sample. Our results reinforce both previous findings and theoretical expectation that galactic bars play a crucial role in the secular evolution of galaxies by driving gas inflow and enhancing the star formation and bulge growth in the centre.

scholarly journals Secular evolution in galaxies

2006 ◽  
Vol 2 (S235) ◽  
pp. 19-23 ◽  
Author(s):  
F. Combes
Keyword(s):  
Star Formation ◽  
Numerical Simulations ◽  
Significant Role ◽  
High Frequency ◽  
Central Star ◽  
Barred Galaxies ◽  
Secular Evolution ◽  
Gas Accretion ◽  
Bar Formation

AbstractNew observations in favour of a significant role of secular evolution are reviewed: central star formation boosted in pseudo-bulge barred galaxies, relations between bulge and disk, evidence for rejuvenated bulges. Numerical simulations have shown that secular evolution can occur through a cycle of bar formation and destruction, in which the gas plays a major role. Since bars are weakened or destroyed in gaseous disks, the high frequency of bars observed today requires external cold gas accretion, to replenish the disk and allow a new bar formation. The rate of gas accretion from external filaments is compatible with what is observed in cosmological simulations.

scholarly journals Feeding and feedback in nearby AGN – comparison with the Milky Way center

2013 ◽  
Vol 9 (S303) ◽  
pp. 354-363 ◽  
Author(s):  
T. Storchi-Bergmann
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Galactic Center ◽  
Formation Rate ◽  
Activity Cycle ◽  
Nuclear Region ◽  
Nuclear Activity ◽  
The Galaxy ◽  
Mass Outflow ◽  
Sgr A

AbstractI discuss feeding and feedback processes observed in the inner few hundred parsecs of nearby active galaxies using integral field spectroscopy at spatial resolutions of a few to tens of parsecs. Signatures of feedback include outflows from the nucleus with velocities ranging from 200 to 1000 km s−1, with mass outflow rates between 0.5 and a few M⊙ yr−1. Signatures of feeding include the observation of gas inflows along nuclear spirals and filaments, with velocities ranging from 50 to 100 km s−1 and mass flow rates from 0.1 to ∼1 M⊙ yr−1. These rates are 2–3 orders of magnitude larger than the mass accretion rate to the supermassive black hole (SMBH). These inflows can thus lead, during less than one activity cycle, to the accumulation of enough gas in the inner few hundred parsecs, to trigger the formation of new stars, leading to the growth of the galaxy bulge. Young to intermediate age stars have indeed been found in circumnuclear rings around a number of Active Galactic Nuclei (AGN). In particular, one of these rings, with radius of ≈ 100 pc is observed in the Seyfert 2 galaxy NGC 1068, and is associated to an off-centered molecular ring, very similar to that observed in the Milky Way (MW). On the basis of an evolutionary scenario in which gas falling into the nuclear region triggers star formation followed by the triggering of nuclear activity, we speculate that, in the case of the MW, molecular gas has already accumulated within the inner ≈ 100 pc to trigger the formation of new stars, as supported by the presence of blue stars close to the galactic center. A possible increase in the star-formation rate in the nuclear region will then be followed, probably tens of millions of years later, by the triggering of nuclear activity in Sgr A*.

scholarly journals The role of spiral arms in Milky Way star formation

2018 ◽  
Vol 479 (2) ◽  
pp. 2361-2373 ◽  
Author(s):  
S E Ragan ◽  
T J T Moore ◽  
D J Eden ◽  
M G Hoare ◽  
J S Urquhart ◽  
...  
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Spiral Arms

scholarly journals What Can We Learn from the Local Group About the Role of Interactions in Galaxy Formation

1999 ◽  
Vol 186 ◽  
pp. 23-29
Author(s):  
K.C. Freeman
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Milky Way ◽  
Local Group ◽  
High Redshift ◽  
Dissipative Process ◽  
Active Star ◽  
Flat Systems ◽  
Active Star Formation

This talk is mainly about the halos and bulges of Local Group galaxies, in particular those of the Milky Way and M31, and what they can tell us about the role of interactions in galaxy formation. Bulges are potentially of particular interest for galaxy formation because they are widely suspected to be the seeds for galaxy formation. Sites of active star formation at high redshift are often regarded as spheroids in the process of formation. In this talk, I will say little about disks because their formation is conceptually understood, although many details remain uncertain. To form such flat systems, a fairly undisturbed dissipative process is needed. This process occurred fairly early: the disks appear to be in place by a redshift z = 1 (Ellis 1997), with a distribution of scalelengths that is similar to the distribution at z = 0.

Role of environment on AGN activity

2019 ◽  
Vol 15 (S356) ◽  
pp. 171-171
Author(s):  
Amirnezam Amiri
Keyword(s):  
Star Formation ◽  
Active Galactic Nuclei ◽  
Galaxy Clusters ◽  
Galactic Nuclei ◽  
Stellar Mass ◽  
Local Universe ◽  
Nuclear Activity ◽  
Star Forming ◽  
Star Formation Activity

AbstractMotivated by the apparently conflicting results reported in the literature on the effect of environment on nuclear activity, we have carried out a new analysis by comparing the fraction of galaxies hosting active galactic nuclei (AGNs) in the most overdense regions (rich galaxy clusters) and the most underdense ones (voids) in the local universe. Exploiting the classical BPT diagnostics, we have extracted volume limited samples of star forming and AGN galaxies. We find that, at variance with star-forming galaxies, AGN galaxies have similar distributions of specific star formation rates and of galactic ages (as indicated by the Dn4000 parameter) both in clusters and in voids. In both environments galaxies hosting AGNs are generally old, with low star formation activity. The AGN fraction increases faster with stellar mass in clusters than in voids, especially above 1010.2 M⊙. Our results indicate that, in the local universe, the nuclear activity correlates with stellar mass and galaxy morphology and is weakly, if at all, affected by the local galaxy density.

scholarly journals The Starburst – AGN Connection: a Critical Review

2011 ◽  
Vol 20 (3) ◽  
Author(s):  
P. Rafanelli ◽  
G. La Mura ◽  
D. Bindoni ◽  
S. Ciroi ◽  
V. Cracco ◽  
...  
Keyword(s):  
Star Formation ◽  
Active Galaxies ◽  
Host Galaxy ◽  
Nuclear Activity ◽  
Massive Black Holes ◽  
Star Forming ◽  
Spectral Signatures ◽  
Star Formation Activity ◽  
Nuclear Regions

AbstractNuclear activity and star formation processes represent two key elements in the evolution of galaxies across the cosmic ages. In spite of very different physical backgrounds, several arguments suggest that they should be closely connected. On the basis of simple theoretical considerations, the transport of appreciable amounts of fuel to the AGN scale is very likely to trigger star formation in the gas. Young stellar populations, in their turn, are expected to affect the properties of the interstellar medium, leading to a complex balance of interactions among nuclear activity and star formation. This scenario is also supported by the observation of super-massive black holes and host galaxy properties, which strongly suggest a common evolutionary track. However, despite several years of extensive investigation, the relationship among the two processes still has to be properly explained. Here we provide a review of some of the most important observations, which are relevant to the issue of the connection among AGN and starburst events. Based on a wide sample of observations, we present an analysis of the spectral signatures connected with AGN and star formation activity. Expanding the concept of the distinction among star forming galaxies and the true active nuclei, we provide systematic evidence for a role of recent starburst events in the circum-nuclear regions of active galaxies and discuss the possibility of its influence onto the AGN environment. We also analyze the age, mass and metallicity properties of star-forming and active galaxies, illustrating that they are arranged in a sequence that is consistent with the identified relation.

The role of interstellar filaments in shaping the IMF and regulating star formation

2015 ◽  
Vol 75-76 ◽  
pp. 137-141
Author(s):  
P. André ◽  
V. Könyves ◽  
A. Roy
Keyword(s):  
Star Formation ◽  
The Imf

The So-Called Prothetic i- and the sḏm-f Paradigms II: The “Nominal” sḏm-f and a Reappraisal

2020 ◽  
Vol 28 ◽  
pp. 259-267
Author(s):  
Sami Uljas
Keyword(s):  
Present Author ◽  
Textual Data ◽  
Key Issues ◽  
Syllabic Structure ◽  
The Creation ◽  
Partial Revision

This article discusses, first, the role of the i-prefix in the so-called “nominal” sḏm-f paradigm in earliest Old Egyptian textual data. It is argued that this represented a means of facilitating the creation of a distinctive syllabic structure with 2rad roots and of harmonising it with that of the 2red and 3inf classes. Second, the study contains a partial revision of some of the key issues treated in an earlier article by the present author on the role of the similarly written prefix in the subjunctive and “circumstantial” sḏm-f paradigms.

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