The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band Hα + NII imaging survey carried out with MegaCam at the Canada-France-Hawaii Telescope. During pilot ...observations taken in the spring of 2016 we observed NGC 4330, an intermediate mass (M* ≃ 109.8 M⊙) edge-on star forming spiral currently falling into the core of the Virgo cluster. While previous Hα observations showed a clumpy complex of ionised gas knots outside the galaxy disc, new deep observations revealed a low surface brightness ~10 kpc tail exhibiting a peculiar filamentary structure. The filaments are remarkably parallel to one another and clearly indicate the direction of motion of the galaxy in the Virgo potential. Motivated by the detection of these features which indicate ongoing gas stripping, we collected literature photometry in 15 bands from the far-UV to the far-IR and deep optical long-slit spectroscopy using the FORS2 instrument at the ESO Very Large Telescope. Using a newly developed Monte Carlo code that jointly fits spectroscopy and photometry, we reconstructed the star formation histories in apertures along the major axis of the galaxy. Our results have been validated against the output of CIGALE, a fitting code which has been previously used for similar studies. We found a clear outside-in gradient with radius of the time when the quenching event started: the outermost radii were stripped ~500 Myr ago, while the stripping reached the inner 5 kpc from the centre in the last 100 Myr. Regions at even smaller radii are currently still forming stars fueled by the presence of HI and H2 gas. When compared to statistical studies of the quenching timescales in the local Universe we find that ram pressure stripping of the cold gas is an effective mechanism to reduce the transformation times for galaxies falling into massive clusters. Future systematic studies of all the active galaxies observed by VESTIGE in the Virgo cluster will extend these results to a robust statistical framework.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
ABSTRACT
We present optical VLT/MUSE integral field spectroscopy data of the merging galaxy NGC 1487. We use fitting techniques to study the ionized gas emission of this merger and its main ...morphological and kinematical properties. We measured flat and sometimes inverted oxygen abundance gradients in the subsystems composing NGC 1487, explained by metal mixing processes common in merging galaxies. We also measured widespread star-forming bursts, indicating that photoionization by stars is the primary ionization source of the galaxy. The kinematic map revealed a rotating pattern in the gas in the northern tail of the system, suggesting that the galaxy may be in the process of rebuilding a disc. The gas located in the central region has larger velocity dispersion (σ ≈ 50 km s−1) than the remaining regions, indicating kinematic heating, possibly owing to the ongoing interaction. Similar trends were, however, not observed in the stellar velocity dispersion map, indicating that the galaxy has not yet achieved equilibrium, and the nebular and stellar components are still kinematically decoupled. Based on all our measurements and findings, and specially on the mass estimates, metallicity gradients, and velocity fields of the system, we propose that NGC 1487 is the result of an ongoing merger event involving smallish dwarf galaxies within a group, in a pre-merger phase, resulting in a relic with mass and physical parameters similar to a dwarf galaxy. Thus, we may be witnessing the formation of a dwarf galaxy by merging of smaller clumps at z = 0.
Context. The Lyα line is an important diagnostic for star formation at high redshift, but interpreting its flux and line profile is difficult because of the resonance nature of Lyα. Trends between ...the escape of Lyα photons and dust and properties of the interstellar medium (ISM) have been found, but detailed comparisons between Lyα emission and the properties of the gas in local high-redshift analogs are vital for understanding the relation between Lyα emission and galaxy properties. Aims. For the first time, we can directly infer the properties of the ionized gas at the same location and similar spatial scales of the extended Lyα halo around the local Lyα emitter and Lyman-break galaxy analog ESO 338-IG04. Methods. We obtained VLT/MUSE integral field spectra. We used ionization parameter mapping of the S ii/O iii line ratio and the kinematics of Hα to study the ionization state and kinematics of the ISM of ESO 338-IG04. Results. The velocity map reveals two outflows, one toward the north, the other toward the south of ESO 338. The ionization parameter mapping shows that the entire central area of the galaxy is highly ionized by photons leaking from the H ii regions around the youngest star clusters. Three highly ionized cones have been identified, of which one is associated with an outflow detected in the Hα. We propose a scenario where the outflows are created by mechanical feedback of the older clusters, while the highly ionized gas is caused by the hard ionizing photons emitted by the youngest clusters. A comparison with the Lyα map shows that the (approximately bipolar) asymmetries observed in the Lyα emission are consistent with the base of the outflows detected in Hα. No clear correlation with the ionization cones is found. Conclusions. The mechanical and ionization feedback of star clusters significantly changes the state of the ISM by creating ionized cones and outflows. The comparison with Lyα suggests that especially the outflows could facilitate the escape of Lyα photons.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
Context.
Malin 1 is the largest known low surface brightness (LSB) galaxy, the archetype of so-called giant LSB galaxies. The structure and origin of such galaxies are still poorly understood, ...especially because of the lack of high-resolution kinematics and spectroscopic data.
Aims.
We use emission lines from spectroscopic observations of Malin 1 aiming to bring new constraints on the internal dynamics and star formation history of Malin 1.
Methods.
We extracted a total of 16 spectra from different regions of Malin 1 and calculated the rotational velocities of these regions from the wavelength shifts and star formation rates from the observed H
α
emission line fluxes. We compared our data with existing data and models for Malin 1.
Results.
For the first time we present the inner rotation curve of Malin 1, characterised in the radial range
r
< 10 kpc by a steep rise in the rotational velocity up to at least ∼350 km s
−1
(with a large dispersion), which had not been observed previously. We used these data to study a suite of new mass models for Malin 1. We show that in the inner regions dynamics may be dominated by the stars (although none of our models can explain the highest velocities measured) but that at large radii a massive dark matter halo remains necessary. The H
α
fluxes derived star formation rates are consistent with an early-type disc for the inner region and with the level found in extended UV galaxies for the outer parts of the giant disc of Malin 1. We also find signs of high metallicity but low dust content for the inner regions.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
ABSTRACT At z 1, the distinction between merging and "normal" star-forming galaxies based on single band morphology is often hampered by the presence of large clumps which result in a disturbed, ...merger-like appearance even in rotationally supported disks. In this paper we discuss how a classification based on canonical, non-parametric structural indices measured on resolved stellar mass maps, rather than on single-band images, reduces the misclassification of clumpy but not merging galaxies. We calibrate the mass-based selection of mergers using the MIRAGE hydrodynamical numerical simulations of isolated and merging galaxies which span a stellar mass range of 109.8-1010.6 M and merger ratios between 1:1-1:6.3. These simulations are processed to reproduce the typical depth and spatial resolution of observed Hubble Ultra Deep Field (HUDF) data. We test our approach on a sample of real galaxies with kinematic classification into disks or mergers and on ∼100 galaxies in the HUDF field with photometric/spectroscopic redshift between 1.5 ≤ z ≤ 3 and M > 109.4 M . We find that a combination of the asymmetry AMASS and M20, MASS indices measured on the stellar mass maps can efficiently identify real (major) mergers with 20% contamination from clumpy disks in the merger sample. This mass-based classification cannot be reproduced in star-forming galaxies by H-band measurements alone, which instead result in a contamination from clumpy galaxies which can be as high as 50%. Moreover, we find that the mass-based classification always results in a lower contamination from clumpy galaxies than an H-band classification, regardless of the depth of the imaging used (e.g., CANDELS versus HUDF).
A precise derivation of the evolution of the Tully Fisher is crucial to understand the interplay between dark matter and baryonic matter in cosmological models, using 15 deployable integral field ...units of FLAMES/GIRAFFE at VLT, we have recovered the velocity fields of 35 galaxies at intermediate redshift (0.4 < z < 0.75). This facility is able to recover the velocity fields of almost all the emission line galaxies with IAB=15 Å. In our sample, we find only 35% rotating disks. These rotating disks produce a Tully-Fisher relationship (stellar mass or MK versus Vmax) which has apparently not evolved in slope, zero point and scatter since z=0.6. The only evolution found is a brightening of the B band luminosity of a third of the disks, possibly due to an enhancement of the star formation. The very large scatters found in previously reported Tully-Fisher relationships at moderate redshifts are caused by the numerous (65%) galaxies with perturbed or complex kinematics. Those galaxies include minor or major mergers, merger remnants and/or inflow/outflows and their kinematics can be easily misidentified by slit spectroscopy. Their presence suggests a strong evolution in the dynamical properties of galaxies during the last 7 Gyr.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
We studied, for the first time, the near-infrared, stellar and baryonic Tully-Fisher relations for a sample of field galaxies taken from a homogeneous Fabry-Perot sample of galaxies the Gassendi ...HAlpha survey of SPirals (GHASP) survey. The main advantage of GHASP over other samples is that the maximum rotational velocities were estimated from 2D velocity fields, avoiding assumptions about the inclination and position angle of the galaxies. By combining these data with 2MASS photometry, optical colours, H i masses and different mass-to-light ratio estimators, we found a slope of 4.48 ± 0.38 and 3.64 ± 0.28 for the stellar and baryonic Tully-Fisher relation, respectively. We found that these values do not change significantly when different mass-to-light ratio recipes were used. We also point out, for the first time, that the rising rotation curves as well as asymmetric rotation curves show a larger dispersion in the Tully-Fisher relation than the flat ones or the symmetric ones. Using the baryonic mass and the optical radius of galaxies, we found that the surface baryonic mass density is almost constant for all the galaxies of this sample. In this study we also emphasize the presence of a break in the NIR Tully-Fisher relation at M
H, K
∼−20 and we confirm that late-type galaxies present higher total-to-baryonic mass ratios than early-type spirals, suggesting that supernova feedback is actually an important issue in late-type spirals. Due to the well-defined sample selection criteria and the homogeneity of the data analysis, the Tully-Fisher relation for GHASP galaxies can be used as a reference for the study of this relation in other environments and at higher redshifts.
The estimate of radial abundance gradients in high-redshift galaxies allows to constrain their star formation history and their interplay with the surrounding intergalactic medium. The authors ...present VLT/SINFONI integral-field spectroscopy of a first sample of 50 galaxies at z similar to 1.2 in the MASSIV survey. Using the N2 ratio between the NII 6584 and H alpha rest-frame optical emission lines as a proxy for oxygen abundance in the interstellar medium, they measured the metallicity of the sample galaxies. Seven galaxies display a positive gradient at a high confidence level. Four out of these are interacting, and one is a chain galaxy. They suggest that interactions might be responsible for shallowing and even inverting the abundance gradient. They also identify two interesting correlations in their sample: galaxies with higher gas velocity dispersion have shallower/positive gradients; and metal-poor galaxies tend to show a positive gradient, whereas metal-rich ones tend to show a negative one.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
We present the Fabry–Perot observations obtained for a new set of 108 galaxies in the frame of the Gassendi Hα survey of SPirals (GHASP). The GHASP survey consists of 3D Hα data cubes for 203 spiral ...and irregular galaxies, covering a large range in morphological types and absolute magnitudes, for kinematics analysis. The new set of data presented here completes the survey. The GHASP sample is by now the largest sample of Fabry–Perot data ever published. The analysis of the whole GHASP sample will be done in forthcoming papers. Using adaptive binning techniques based on Voronoi tessellations, we have derived Hα data cubes from which are computed Hα maps, radial velocity fields as well as residual velocity fields, position–velocity diagrams, rotation curves and the kinematical parameters for almost all galaxies. Original improvements in the determination of the kinematical parameters, rotation curves and their uncertainties have been implemented in the reduction procedure. This new method is based on the whole 2D velocity field and on the power spectrum of the residual velocity field rather than the classical method using successive crowns in the velocity field. Among the results, we point out that morphological position angles have systematically higher uncertainties than kinematical ones, especially for galaxies with low inclination. The morphological inclination of galaxies having no robust determination of their morphological position angle cannot be constrained correctly. Galaxies with high inclination show a better agreement between their kinematical inclination and their morphological inclination computed assuming a thin disc. The consistency of the velocity amplitude of our rotation curves has been checked using the Tully–Fisher relationship. Our data are in good agreement with previous determinations found in the literature. Nevertheless, galaxies with low inclination have statistically higher velocities than expected and fast rotators are less luminous than expected.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
PDF
