30 research outputs found
Widespread star formation inside galactic outflows
Several models have predicted that stars could form inside galactic outflows
and that this would be a new major mode of galaxy evolution. Observations of
galactic outflows have revealed that they host large amounts of dense and
clumpy molecular gas, which provide conditions suitable for star formation. We
have investigated the properties of the outflows in a large sample of galaxies
by exploiting the integral field spectroscopic data of the large MaNGA-SDSS4
galaxy survey. We find that star formation occurs inside at least half of the
galactic outflows in our sample. We also show that even if star formation is
prominent inside many other galactic outflows, this may have not been revealed
as the diagnostics are easily dominated by the presence of even faint AGN and
shocks. If very massive outflows typical of distant galaxies and quasars follow
the same scaling relations observed locally, then the star formation inside
high-z outflows can be up to several 100 Msun/yr and could contribute
substantially to the early formation of the spheroidal component of galaxies.
Star formation in outflows can also potentially contribute to establishing the
scaling relations between black holes and their host spheroids. Moreover,
supernovae exploding on large orbits can chemically enrich in-situ and heat the
circumgalactic and intergalactic medium. Finally, young stars ejected on large
orbits may also contribute to the reionization of the Universe
Mildly suppressed star formation in central regions of MaNGA Seyfert galaxies
Negative feedback from accretion onto super-massive black holes (SMBHs), that
is to remove gas and suppress star formation in galaxies, has been widely
suggested. However, for Seyfert galaxies which harbor less active, moderately
accreting SMBHs in the local universe, the feedback capability of their black
hole activity is elusive. We present spatially-resolved H measurements
to trace ongoing star formation in Seyfert galaxies and compare their specific
star formation rate with a sample of star-forming galaxies whose global galaxy
properties are controlled to be the same as the Seyferts. From the comparison
we find that the star formation rates within central kpc of Seyfert galaxies
are mildly suppressed as compared to the matched normal star forming galaxies.
This suggests that the feedback of moderate SMBH accretion could, to some
extent, regulate the ongoing star formation in these intermediate to late type
galaxies under secular evolution.STFC
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The multiphase gas structure and kinematics in the circumnuclear region of NGC 5728
We report on our combined analysis of HST, VLT/MUSE, VLT/SINFONI, and ALMA observations of the local Seyfert 2 galaxy, NGC 5728 to investigate in detail the feeding and feedback of the active galactic nucleus (AGN). The data sets simultaneously probe the morphology, excitation, and kinematics of the stars, ionized gas, and molecular gas over a large range of spatial scales (10 pc to 10 kpc). NGC 5728 contains a large stellar bar that is driving gas along prominent dust lanes to the inner 1 kpc where the gas settles into a circumnuclear ring. The ring is strongly star forming and contains a substantial population of young stars as indicated by the lowered stellar velocity dispersion and gas excitation consistent with H II regions. We model the kinematics of the ring using the velocity field of the CO (2–1) emission and stars and find it is consistent with a rotating disc. The outer regions of the disc, where the dust lanes meet the ring, show signatures of inflow at a rate of 1 M⊙ yr−1. Inside the ring, we observe three molecular gas components corresponding to the circular rotation of the outer ring, a warped disc, and the nuclear stellar bar. The AGN is driving an ionized gas outflow that reaches a radius of 250 pc with a mass outflow rate of 0.08 M⊙ yr−1 consistent with its luminosity and scaling relations from previous studies. While we observe distinct holes in CO emission which could be signs of molecular gas removal, we find that largely the AGN is not disrupting the structure of the circumnuclear region
Do stellar winds play a decisive role in feeding AGN?
While the existence of a starburst-AGN connection is undisputed, there is no
consensus on what the connection is. In this contribution, we begin by noting
that the mechanisms which drive gas inwards in disk galaxies are generally
inefficient at removing angular momentum, leading to stalled inflows. Thus, a
tiered series of such processes is required to bring gas to the smallest
scales, each of which on its own may not correlate with the presence of an AGN.
Similarly, each may be associated with a starburst event, making it important
to discriminate between 'circumnuclear' and 'nuclear' star formation. In this
contribution, we show that stellar feedback on scales of tens of parsecs plays
a critical role in first hindering and then helping accretion. We argue that it
is only after the initial turbulent phases of a starburst that gas from slow
stellar winds can accrete efficiently to smaller scales. This would imply that
the properties of the obscuring torus are directly coupled to star formation
and that the torus must be a complex dynamical entity. We finish by remarking
on other contexts where similar processes appear to be at work.Comment: to appear in 'The central kiloparsec in Galactic Nuclei', Journal of
Physics: Conference Series (JPCS), IOP Publishin
SDSS-IV MaNGA: A serendipitous observation of a potential gas accretion event
The nature of warm, ionized gas outside of galaxies may illuminate several key galaxy evolutionary processes. A serendipitous observation by the MaNGA survey has revealed a large, asymmetric H complex with no optical counterpart that extends ≈8″ (≈6.3 kpc) beyond the effective radius of a dusty, starbursting galaxy. This H extension is approximately three times the effective radius of the host galaxy and displays a tail-like morphology. We analyze its gas-phase metallicities, gaseous kinematics, and emission-line ratios and discuss whether this H extension could be diffuse ionized gas, a gas accretion event, or something else. We find that this warm, ionized gas structure is most consistent with gas accretion through recycled wind material, which could be an important process that regulates the low-mass end of the galaxy stellar mass function.Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration. D.B. is supported by grant RSCF-14-22-00041. A.W. acknowledges support from a Leverhulme Early Career Fellowship. J.H.K. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under grant number AYA2013-41243-P and thanks the Astrophysics Research Institute of Liverpool John Moores University for their hospitality, and the Spanish Ministry of Education, Culture and Sports for financial support of his visit there, through grant number PR2015-00512
Ionized outflows in local luminous AGN: what are the real densities and outflow rates?
We report on the determination of electron densities, and their impact on the outflow masses and rates, measured in the central few hundred parsecs of 11 local luminous active galaxies. We show that the peak of the integrated line emission in the active galactic nuclei (AGN) is significantly offset from the systemic velocity as traced by the stellar absorption features, indicating that the profiles are dominated by outflow. In contrast, matched inactive galaxies are characterized by a systemic peak and weaker outflow wing. We present three independent estimates of the electron density in these AGN, discussing the merits of the different methods. The electron density derived from the [S II] doublet is significantly lower than that found with a method developed in the last decade using auroral and transauroral lines, as well as a recently introduced method based on the ionization parameter. The reason is that, for gas photoionized by an AGN, much of the [S II] emission arises in an extended partially ionized zone where the implicit assumption that the electron density traces the hydrogen density is invalid. We propose ways to deal with this situation and we derive the associated outflow rates for ionized gas, which are in the range 0.001–0.5 M⊙ yr−1 for our AGN sample. We compare these outflow rates to the relation between ˙M out and LAGN in the literature, and argue that it may need to be modified and rescaled towards lower mass outflow rates
Insights on the Dusty Torus and Neutral Torus From Optical and X-Ray Obscuration in A Complete Volume Limited Hard X-Ray Agn Sample
We describe a complete volume limited sample of nearby active galaxies selected by their 14–195 keV luminosity, and outline its rationale for studying the mechanisms regulating gas inflow and outflow. We also describe a complementary sample of inactive galaxies, selected to match the host galaxy properties. The active sample appears to have no bias in terms of active galactic nucleus (AGN) type, the only difference being the neutral absorbing column, which is two orders of magnitude greater for the Seyfert 2s. In the luminosity range spanned by the sample, –43.7, the optically obscured and X-ray absorbed fractions are 50%–65%. The similarity of these fractions to more distant spectroscopic AGN samples, although over a limited luminosity range, suggests that the torus does not strongly evolve with redshift. Our sample confirms that X-ray unabsorbed Seyfert 2s are rare, comprising not more than a few percent of the Seyfert 2 population. At higher luminosities, the optically obscured fraction decreases (as expected for the increasing dust sublimation radius), but the X-ray absorbed fraction changes little. We argue that the cold X-ray absorption in these Seyfert 1s can be accounted for by neutral gas in clouds that also contribute to the broad-line region (BLR) emission, and suggest that a geometrically thick neutral gas torus co-exists with the BLR and bridges the gap to the dusty torus
Vaccinia Virus Proteins A52 and B14 Share a Bcl-2–Like Fold but Have Evolved to Inhibit NF-κB rather than Apoptosis
Vaccinia virus (VACV), the prototype poxvirus, encodes numerous proteins that modulate the host response to infection. Two such proteins, B14 and A52, act inside infected cells to inhibit activation of NF-κB, thereby blocking the production of pro-inflammatory cytokines. We have solved the crystal structures of A52 and B14 at 1.9 Å and 2.7 Å resolution, respectively. Strikingly, both these proteins adopt a Bcl-2–like fold despite sharing no significant sequence similarity with other viral or cellular Bcl-2–like proteins. Unlike cellular and viral Bcl-2–like proteins described previously, A52 and B14 lack a surface groove for binding BH3 peptides from pro-apoptotic Bcl-2–like proteins and they do not modulate apoptosis. Structure-based phylogenetic analysis of 32 cellular and viral Bcl-2–like protein structures reveals that A52 and B14 are more closely related to each other and to VACV N1 and myxoma virus M11 than they are to other viral or cellular Bcl-2–like proteins. This suggests that a progenitor poxvirus acquired a gene encoding a Bcl-2–like protein and, over the course of evolution, gene duplication events have allowed the virus to exploit this Bcl-2 scaffold for interfering with distinct host signalling pathways
Protein disulphide isomerase-assisted functionalization of proteinaceous substrates
Protein disulphide isomerase (PDI) is an enzyme that catalyzes thiol-disulphide exchange reactions among a broad spectrum of substrates, including proteins and low-molecular thiols and disulphides. As the first protein-folding catalyst reported, the study of PDI has mainly involved the correct folding of several cysteine-containing proteins. Its application on the functionalization of protein-based materials has not been extensively reported. Herein, we review the applications of PDI on the modification of proteinaceous substrates and discuss its future potential. The mechanism involved in PDI functionalization of fibrous protein substrates is discussed in detail. These approaches allow innovative applications in textile dyeing and finishing, medical textiles, controlled drug delivery systems and hair or skin care products.We thank to FCT 'Fundacao para a Ciencia e Tecnologia' (scholarship SFRH/BD/38363/2007) for providing Margarida Fernandes the grant for PhD studies