Context. In Λ-CDM models, galaxies are thought to grow both through continuous cold gas accretion coming from the cosmic web and episodic merger events. The relative importance of these different ...mechanisms at different cosmic epochs is nevertheless not yet understood well. Aims. We aim to address questions related to galaxy mass assembly through major and minor wet merging processes in the redshift range 1 < z < 2, an epoch that corresponds to the peak of cosmic star formation history. A significant fraction of Milky Way-like galaxies are thought to have undergone an unstable clumpy phase at this early stage. We focus on the behavior of the young clumpy disks when galaxies are undergoing gas-rich galaxy mergers. Methods. Using the adaptive mesh-refinement code RAMSES, we build the Merging and Isolated high redshift Adaptive mesh refinement Galaxies (MIRAGE) sample. It is composed of 20 mergers and 3 isolated idealized disks simulations, which sample disk orientations and merger masses. Our simulations can reach a physical resolution of 7 parsecs, and include star formation, metal line cooling, metallicity advection, and a recent physically-motivated implementation of stellar feedback that encompasses OB-type stars radiative pressure, photo-ionization heating, and supernovae. Results. The star formation history of isolated disks shows a stochastic star formation rate, which proceeds from the complex behavior of the giant clumps. Our minor and major gas-rich merger simulations do not trigger starbursts, suggesting a saturation of the star formation due to the detailed accounting of stellar feedback processes in a turbulent and clumpy interstellar medium fed by substantial accretion from the circumgalactic medium. Our simulations are close to the normal regime of the disk-like star formation on a Schmidt-Kennicutt diagram. The mass–size relation and its rate of evolution in the redshift range 1 < z < 2 matches observations, suggesting that the inside-out growth mechanisms of the stellar disk do not necessarily require cold accretion.
This study presents a deep Hα kinematical analysis of the Sculptor Group galaxy NGC 253. The Fabry-Perot data were taken with the 36-cm Marseille Telescope in La Silla, Chile, using an EMCCD ...detector. Typical emission measures of ∼0.1 cm−6 pc are reached. The observations allow the detection of the diffuse ionized gas component through N ii emission at very large radii of 11.5, 12.8 and 19.0 arcmin, on the receding side of the galaxy. No Hα emission is observed at radii larger than the neutral component (11.5 arcmin). The very extended rotation curve confirms previous results and shows signs of a significant decline, on the order of 30 per cent v
max. Using the rotation data, mass models are constructed with and without the outer N ii data points, and similar results are found. The declining part of the rotation curve is very well modelled, and seems to be truly declining.
Mass models of 100 nearby spiral and irregular galaxies, covering morphological types from Sa to Irr, are computed using Hα rotation curves and R c-band surface brightness profiles. The kinematics ...was obtained using a scanning Fabry-Perot interferometer. One of the aims is to compare our results with those from Korsaga et al. (2018), which used mid-infrared (MIR) WISE W1 (3.4 µm) photometric data. For the analysis, the same tools were used for both bands. Pseudo-Isothermal (ISO) core and Navarro-Frenk-White (NFW) cuspy models have been used. We test Best Fit Models (BFM), Maximum Disc Models (MDM) and models for which M/L is fixed using the B-V colors. Similarly to what was found in the MIR 3.4 µm band, most of the observed rotation curves are better described by a central core density profile (ISO) than a cuspy one (NFW) when using the optical R c-band. In both bands, the dispersion in the (M/L) values is smaller for the fixed M/L fits. As for the W1 photometry, the derived DM halos' parameters depend on the morphological types. We find similar relations than those in the literature, only when we compare our results for the bulge-poor sub-sample because most of previous results were mainly based on late-type spirals. Because the dispersion in the model parameters is smaller and because stellar masses are better defined in that band, MIR photometry should be preferred, when possible, to the optical bands. It is shown that for high-z galaxies, sensible results can still be obtained without full profile decomposition.
We present the integrated Hα emission line profile for 157 H ii regions in the central 3.4 × 3.4 arcmin2 of the galaxy M83 (NGC 5236). Using the Fabry–Perot interferometer GHαFaS, on the 4.2-m ...William Herschel Telescope on La Palma, we show the importance of a good characterization of the instrumental response function for the study of line profile shapes. The luminosity–velocity dispersion relation is also studied, and in the log(L)–log(σ) plane we do not find a linear relation, but an upper envelope with equation log(LHα) = 0.9 log(σ) + 38.1. For the adopted distance of 4.5 Mpc, the upper envelope appears at the luminosity L= 1038.5 erg s−1, in full agreement with previous studies of other galaxies, reinforcing the idea of using H ii regions as standard candles.
GHαFaS, a new Fabry-Perot system, is now available at the William Herschel Telescope (WHT). It was mounted, for the first time, at the Nasmyth focus of the 4.2-m WHT on La Palma in 2007 July. Using ...modern technology, with a spectral resolution of the orderR ∼ 15,000
R
∼
15
,
000
, and with a seeing-limited spatial resolution, GHαFaSwill provide a new look at the Hα-emitting gas over a 4.8′ circular field in the nearby universe. Many science programs can be done on a 4.2-m class telescope in world-class seeing conditions with a scanning Fabry-Perot. Not only galaxies but H IIregions, planetary nebulae, supernova remnants, and the diffuse interstellar medium are subjects for which unique data can be aquired rapidly. Astronomers from the Laboratoire d’Astrophysique Expérimentale (LAE) in Montréal, the Laboratoire d’Astrophysique de Marseille (LAM-OAMP), and the Instituto de Astrofísica de Canarias (IAC), have inaugurated GHαFaSby studying in detail the dynamics of some nearby spiral galaxies. A robust set of state-of-the-art tools for reducing and analyzing the data cubes obtained with GHαFaShas also been developed.
Aims.
At intermediate redshift, galaxy groups and clusters are thought to impact galaxy properties such as their angular momentum. We investigate whether the environment has an impact on the ...galaxies’ stellar angular momentum and identify underlying driving physical mechanisms.
Methods.
We derived robust estimates of the stellar angular momentum using
Hubble
Space Telescope (HST) images combined with spatially resolved ionised gas kinematics from the Multi-Unit Spectroscopic Explorer (MUSE) for a sample of ∼200 galaxies in groups and in the field at
z
∼ 0.7 drawn from the MAGIC survey. Using various environmental tracers, we study the position of the galaxies in the angular momentum–stellar mass (Fall) relation as a function of environment.
Results.
We measured a 0.12 dex (2
σ
significant) depletion of stellar angular momentum for low-mass galaxies (
M
⋆
< 10
10
M
⊙
) located in groups with respect to the field. Massive galaxies located in dense environments have less angular momentum than expected from the low-mass Fall relation but, without a comparable field sample, we cannot infer whether this effect is mass or environmentally driven. Furthermore, these massive galaxies are found in the central parts of the structures and have low systemic velocities. The observed depletion of angular momentum at low stellar mass does not appear linked with the strength of the over-density around the galaxies but it is strongly correlated with (i) the systemic velocity of the galaxies normalised by the dispersion of their host group and (ii) their ionised gas velocity dispersion.
Conclusions.
Galaxies in groups appear depleted in angular momentum, especially at low stellar mass. Our results suggest that this depletion might be induced by physical mechanisms that scale with the systemic velocity of the galaxies (e.g., stripping or merging) and that such a mechanism might be responsible for enhancing the velocity dispersion of the gas as galaxies lose angular momentum.
We study the IB(s)m galaxy IC 3476 observed in the context of the Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE), a blind narrow-band H
α
+NII imaging survey of the Virgo cluster ...carried out with MegaCam at the CFHT. The deep narrow-band image reveals a very pertubed ionised gas distribution that is characterised by a prominent banana-shaped structure in the front of the galaxy formed of giant HII regions crossing the stellar disc. Star-forming structures, at ∼8 kpc from the edges of the stellar disc, are also detected in a deep far-ultraviolet ASTROSAT/UVIT image. This particular morphology indicates that the galaxy is undergoing an almost edge-on ram pressure stripping event. The same H
α
+NII image also shows that the star formation activity is totally quenched in the leading edge of the disc, where the gas has been removed during the interaction with the surrounding medium. The spectral energy distribution fitting analysis of the multi-frequency data indicates that this quenching episode is very recent (∼50 Myr), and roughly corresponds to an increase of the star formation activity by a factor of ∼161% in the inner regions with respect to that expected for secular evolution. The analysis of these data, whose angular resolution enables the study of the induced effects of the perturbation down to the scale of individual HII regions (
r
eq
≃ 40 pc), also suggests that the increase of star formation activity is due to the compression of the gas along the stellar disc of the galaxy, which is able to increase its mean electron density and boost the star formation process producing bright HII regions with luminosities up to
L
(H
α
) ≃ 10
38
erg s
−1
. The combined analysis of the VESTIGE data with deep IFU spectroscopy gathered with MUSE and with high spectral resolution Fabry Perot data also indicates that the hydrodynamic interaction has deeply perturbed the velocity field of the ionised gas component while leaving that of the stellar disc unaffected. The comparison of the data with tuned high-resolution hydrodynamic simulations accounting for the different gas phases (atomic, molecular, ionised) consistently indicates that the perturbing event is very recent (50–150 Myr), once again confirming that ram pressure stripping is a violent phenomenon that is able to perturb the evolution of galaxies in rich environments on short timescales.
Context.
Giant low surface brightness (GLSB) galaxies are an extreme class of objects with very faint and extended gas-rich disks. Malin 1 is the largest GLSB galaxy known to date and one of the ...largest individual spiral galaxies observed so far, but the properties and formation mechanisms of its giant disk are still poorly understood.
Aims.
We used VLT/MUSE IFU spectroscopic observations of Malin 1 to measure the star formation rate (SFR), dust attenuation, and gas metallicity within this intriguing galaxy.
Methods.
We performed a penalized pixel fitting modeling to extract emission line fluxes such as H
α
, H
β
, N
II
6583
and O
III
5007
along the central region as well as from the extended disk of Malin 1.
Results.
Our observations reveal for the first time strong H
α
emission distributed across numerous regions throughout the extended disk of Malin 1. The emission extends to radial distances of ∼100 kpc, which indicates recent star formation activity. We made an estimate of the dust attenuation in the disk of Malin 1 using the Balmer decrement and found that Malin 1 has a mean H
α
attenuation of 0.36 mag. We observe a steep decline in the radial distribution of the SFR surface density (Σ
SFR
) within the inner 20 kpc, followed by a shallow decline in the extended disk. We estimated the gas phase metallicity in Malin 1. We also found for the first time that the metallicity shows a steep gradient from solar metallicity to subsolar values in the inner 20 kpc of the galaxy, followed by a flattening of the metallicity in the extended disk with a relatively high value of ∼0.6
Z
⊙
. We found that the normalized abundance gradient of the inner disk of Malin 1 is similar to the values found in normal galaxies. However, the normalized gradient observed in the outer disk can be considered extreme when compared to other disk galaxies. A comparison of the SFR surface density and gas surface density shows that unlike normal disk galaxies or other low surface brightness galaxies, the outer disk of Malin 1 exhibits a relatively low star formation efficiency based on atomic gas-mass estimates, which may be mildly exacerbated by the vanishing upper molecular gas-mass limits found by recent CO studies.
Conclusions.
With the detection of emission lines in a large part of the extended disk of Malin 1, this work sheds light on the star formation processes in this unique galaxy, highlighting its extended star-forming disk, dust attenuation, almost flat metallicity distribution in the outer disk, and exceptionally low star formation efficiency. Together with previous results, our findings contribute to a more detailed understanding of the formation of the giant disk of Malin 1, and they also constrain possible proposed scenarios of the nature of GLSB galaxies in general.
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