37 research outputs found
Untangling jellyfish galaxies: exploring the kinematic and physical properties of galaxies undergoing hydrodynamical interactions using the new generation of integral field units
Understanding the role and importance of different mechanisms which act to transform and evolve galaxies in the universe is vital in order to build a picture of the lifecycle of galaxies. Many observations over the years have shed light on such processes, both internal to galaxies and resulting from the influence of their environments. In this thesis, the current picture of galaxy evolution will be presented through a review of the literature, narrowing the focus down to a particular process which becomes important within dense environments such as groups and clusters: Ram-pressure stripping. Three studies are subsequently presented which investigate the effect of ram-pressure stripping on a galaxy, uncovering how and from where gas is stripped, the effect of stripping on a galaxyâs star formation and the fate of the gas that is removed from the galaxy. By studying the scope and effectiveness of ram-pressure stripping in great detail on an archetypal jellyfish galaxy, steps are taken towards understanding the importance of the process and its role in transforming galaxies in the universe
GASP XIII. Star formation in gas outside galaxies
Based on MUSE data from the GASP survey, we study the Halpha-emitting
extraplanar tails of 16 cluster galaxies at z~0.05 undergoing ram pressure
stripping. We demonstrate that the dominating ionization mechanism of this gas
(between 64% and 94% of the Halpha emission in the tails depending on the
diagnostic diagram used) is photoionization by young massive stars due to
ongoing star formation (SF) taking place in the stripped tails. This SF occurs
in dynamically quite cold HII clumps with a median Halpha velocity dispersion
sigma = 27 km s^-1. We study the characteristics of over 500 star-forming
clumps in the tails and find median values of Halpha luminosity L_{Halpha} = 4
X 10^38 erg s^-1, dust extinction A_V=0.5 mag, star formation rate SFR=0.003
M_sun yr^-1, ionized gas density n_e =52 cm^-3, ionized gas mass M_gas = 4 X
10^4 Msun, and stellar mass M_{*} = 3 X 10^6 Msun. The tail clumps follow
scaling relations (M_gas-M_{*}, L_{Halpha} -sigma, SFR-M_gas) similar to disk
clumps, and their stellar masses are comparable to Ultra Compact Dwarfs and
Globular Clusters.The diffuse gas component in the tails is ionized by a
combination of SF and composite/LINER-like emission likely due to thermal
conduction or turbulence. The stellar photoionization component of the diffuse
gas can be due either to leakage of ionizing photons from the HII clumps with
an average escape fraction of 18%, or lower luminosity HII regions that we
cannot individually identify.Comment: accepted for publication in MNRA
GASP IV: A muse view of extreme ram-pressure stripping in the plane of the sky: the case of jellyfish galaxy JO204
In the context of the GAs Stripping Phenomena in galaxies with Muse (GASP)
survey, we present the characterization of JO204, a jellyfish galaxy in A957, a
relatively low-mass cluster with . This galaxy
shows a tail of ionized gas that extends up to 30 kpc from the main body in the
opposite direction of the cluster center. No gas emission is detected in the
galaxy outer disk, suggesting that gas stripping is proceeding outside-in. The
stellar component is distributed as a regular disk galaxy; the stellar
kinematics shows a symmetric rotation curve with a maximum radial velocity of
200km/s out to 20 kpc from the galaxy center. The radial velocity of the gas
component in the central part of the disk follows the distribution of the
stellar component; the gas kinematics in the tail retains the rotation of the
galaxy disk, indicating that JO204 is moving at high speed in the intracluster
medium. Both the emission and radial velocity maps of the gas and stellar
components indicate ram-pressure as the most likely primary mechanism for gas
stripping, as expected given that JO204 is close to the cluster center and it
is likely at the first infall in the cluster. The spatially resolved star
formation history of JO204 provides evidence that the onset of ram-pressure
stripping occurred in the last 500 Myr, quenching the star formation activity
in the outer disk, where the gas has been already completely stripped. Our
conclusions are supported by a set of hydrodynamic simulations.Comment: accepted for publication in Ap
GASP III. JO36: a case of multiple environmental effects at play?
The so-called jellyfish galaxies are objects exhibiting disturbed morphology,
mostly in the form of tails of gas stripped from the main body of the galaxy.
Several works have strongly suggested ram pressure stripping to be the
mechanism driving this phenomenon. Here, we focus on one of these objects,
drawn from a sample of optically selected jellyfish galaxies, and use it to
validate SINOPSIS, the spectral fitting code that will be used for the analysis
of the GASP (GAs Stripping Phenomena in galaxies with MUSE) survey, and study
the spatial distribution and physical properties of gas and stellar populations
in this galaxy. We compare the model spectra to those obtained with GANDALF, a
code with similar features widely used to interpret the kinematic of stars and
gas in galaxies from IFU data. We find that SINOPSIS can reproduce the
pixel-by-pixel spectra of this galaxy at least as good as GANDALF does,
providing reliable estimates of the underlying stellar absorption to properly
correct the nebular gas emission. Using these results, we find strong evidences
of a double effect of ram pressure exerted by the intracluster medium onto the
gas of the galaxy. A moderate burst of star formation, dating between 20 and
500 Myr ago and involving the outer parts of the galaxy more strongly than the
inner regions, was likely induced by a first interaction of the galaxy with the
intracluster medium. Stripping by ram pressure, plus probable gas depletion due
to star formation, contributed to create a truncated ionized gas disk. The
presence of an extended stellar tail on only one side of the disk, points
instead to another kind of process, likely a gravitational interaction by a
fly-by or a close encounter with another galaxy in the cluster.Comment: ApJ in press, 26 pages, 18 figure
GASP. XX. From the loose spatially-resolved to the tight global SFR-Mass relation in local spiral galaxies
Exploiting the sample of 30 local star-forming, undisturbed late-type
galaxies in different environments drawn from the GAs Stripping Phenomena in
galaxies with MUSE (GASP), we investigate the spatially resolved Star Formation
Rate-Mass ({\Sigma}SFR-{\Sigma}_star) relation. Our analysis includes also the
galaxy outskirts (up to >4 effective radii, re), a regime poorly explored by
other Integral Field Spectrograph surveys. Our observational strategy allows us
to detect H{\alpha} out to more than 2.7re for 75% of the sample. Considering
all galaxies together, the correlation between the {\Sigma}SFR and
{\Sigma}_star is quite broad, with a scatter of 0.3 dex. It gets steeper and
shifts to higher {\Sigma}_star values when external spaxels are excluded and
moving from less to more massive galaxies. The broadness of the overall
relation suggests galaxy-by-galaxy variations. Indeed, each object is
characterized by a distinct {\Sigma}SFR-{\Sigma}_star relation and in some
cases the correlation is very loose. The scatter of the relation mainly arises
from the existence of bright off-center star-forming knots whose
{\Sigma}SFR-{\Sigma}_star relation is systematically broader than that of the
diffuse component. The {\Sigma}SFR-{\Sigma}tot gas (total gas surface density)
relation is as broad as the {\Sigma}SFR-{\Sigma}_star relation, indicating that
the surface gas density is not a primary driver of the relation. Even though a
large galaxy-by-galaxy variation exists, mean {\Sigma}SFR and {\Sigma}_star
values vary of at most 0.7 dex across galaxies. We investigate the relationship
between the local and global SFR-M_star relation, finding that the latter is
driven by the existence of the size-mass relation.Comment: MNRAS in press, 19 pages, 14 figure
The role of environment on quenching, star formation and AGN activity
Galaxies undergoing ram pressure stripping in clusters are an excellent
opportunity to study the effects of environment on both the AGN and the star
formation activity. We report here on the most recent results from the GASP
survey. We discuss the AGN-ram pressure stripping connection and some evidence
for AGN feedback in stripped galaxies. We then focus on the star formation
activity, both in the disks and the tails of these galaxies, and conclude
drawing a picture of the relation between multi-phase gas and star formation.Comment: Proceedings of the IAU Symposium 359 "Galaxy evolution and feedback
across different environments", editors T. Storchi-Bergmann, R. Overzier, W.
Forman & R. Riffel - final versio
Tales of Tails: Gas Stripping Phenomena in Galaxies with MUSE
The MUSE spectrograph is observing a sample of over 100 galaxies at z = 0.04-0.07 in order to investigate how environmental effects can cause galaxies to lose their gas. These galaxies have a wide range of galaxy stellar masses and environments, from clusters and groups to isolated galaxies, and have been selected because they show unilateral debris or tails suggestive of gas stripping. MUSEâs large field of view, sensitivity, and spatial and spectral resolution allow us to study the physics of the stars and ionised gas in each galaxy in great detail, including the outskirts and extraplanar tails or debris out to 50-100 kpc away from each galaxy: a distance of more than ten times the galaxyâs effective radius. We present the ongoing programme, GAs Stripping Phenomena in galaxies (GASP), and report on the first set of results
Ram pressure feeding super-massive black holes
When supermassive black holes at the center of galaxies accrete matter
(usually gas), they give rise to highly energetic phenomena named Active
Galactic Nuclei (AGN). A number of physical processes have been proposed to
account for the funneling of gas towards the galaxy centers to feed the AGN.
There are also several physical processes that can strip gas from a galaxy, and
one of them is ram pressure stripping in galaxy clusters due to the hot and
dense gas filling the space between galaxies. We report the discovery of a
strong connection between severe ram pressure stripping and the presence of AGN
activity. Searching in galaxy clusters at low redshift, we have selected the
most extreme examples of jellyfish galaxies, which are galaxies with long
tentacles of material extending for dozens of kpc beyond the galaxy disk. Using
the MUSE spectrograph on the ESO Very Large Telescope, we find that 6 out of
the 7 galaxies of this sample host a central AGN, and two of them also have
galactic-scale AGN ionization cones. The high incidence of AGN among the most
striking jellyfishes may be due to ram pressure causing gas to flow towards the
center and triggering the AGN activity, or to an enhancement of the stripping
caused by AGN energy injection, or both. Our analysis of the galaxy position
and velocity relative to the cluster strongly supports the first hypothesis,
and puts forward ram pressure as another, yet unforeseen, possible mechanism
for feeding the central supermassive black hole with gas.Comment: published in Nature, Vol.548, Number 7667, pag.30