arXiv subjects

H. Flores

Publications and source records attributed to H. Flores.

At least 73 records · Page 4Linked to original sources

arXiv2010

Comparing six evolutionary population synthesis models through spectral synthesis on galaxies

We compare six popularly used evolutionary population synthesis (EPS) models (BC03, CB07, Ma05, GALEV, GRASIL, Vazdekis/Miles) through fitting the full optical spectra of six representative types of galaxies (star-forming and composite galaxies, Seyfert 2s, LINERs, E+A and early-type galaxies), which are taken from the Sloan Digital Sky Survey (SDSS). Throughout our paper, we use the simple stellar populations (SSPs) from each EPS model and the software STARLIGHT to do our fits. Our main results are: Using different EPS models the resulted numerical values of contributed light fractions change obviously, even though the dominant populations are consistent. The stellar population synthesis does depend on the selection of age and metallicity, while it does not depend on the stellar evolution track much. The importance of young populations decreases from star-forming, composite, Seyfert 2, LINER to early-type galaxies, and E+A galaxies lie between composite galaxies and Seyfert 2s in most cases. We conclude that different EPS models do derive different stellar populations, so that it is not reasonable to directly compare stellar populations estimated from different EPS models. To get reliable results, we should use the same EPS model for the compared samples.

astro-ph.CO↗

arXiv2010

How was the Hubble sequence 6 Gyrs ago?

The way galaxies assemble their mass to form the well-defined Hubble sequence is amongst the most debated topic in modern cosmology. One difficulty is to link distant galaxies to those at present epoch. We aim at establishing how were the galaxies of the Hubble sequence, 6 Gyrs ago. We intend to derive a past Hubble sequence that can be causally linked to the present-day one. We selected samples of nearby galaxies from the SDSS and of distant galaxies from the GOODS survey. We verified that each sample is representative of galaxies. We further showed that the observational conditions necessary to retrieve their morphological classification are similar in an unbiased way. Morphological analysis has been done in an identical way for all galaxies in the two samples. We found an absence of number evolution for elliptical and lenticular galaxies, which strikingly contrasts with the strong evolution of spiral and peculiar galaxies. Spiral galaxies were 2.3 times less abundant in the past, that is exactly compensated by the strong decrease by a factor 5 of peculiar galaxies. It strongly suggests that more than half of the present-day spirals had peculiar morphologies, 6 Gyrs ago, and this has to be accounted by any scenario of galactic disk evolution and formation. The past Hubble sequence can be used to test these scenarios as well as to test evolution of fundamental planes for spirals and bulges.

astro-ph.CO↗

arXiv2010

GRB 090313: X-shooter's first shot at a GRB

Context. X-shooter is the first second-generation instrument to become operative at the ESO Very Large Telescope (VLT). It is a broad-band medium-resolution spectrograph designed with gamma-ray burst (GRB) afterglow spectroscopy as one of its main science drivers. Aims. During the first commissioning night on sky with the instrument fully assembled, X-shooter observed the afterglow of GRB 090313 as a demonstration of the instrument's capabilities. Methods. GRB 090313 was observed almost two days after the burst onset, when the object had already faded to R~21.6. Furthermore, the 90% illuminated Moon was just 30 degrees away from the field. In spite of the adverse conditions, we obtained a spectrum that, for the first time in GRB research, covers simultaneously the range from 5700 to 23000 Angstroms. Results. The spectrum shows multiple absorption features at a redshift of 3.3736, the redshift of the GRB. These features are composed of 3 components with different ionisation levels and velocities. Some of the features have never been observed before in a GRB at such a high redshift. Furthermore, we detect two intervening systems at redshifts of 1.8005 and 1.9597. Conclusions. These results demonstrate the potential of X-shooter in the GRB field, as it was capable of observing a GRB down to a magnitude limit that would include 72% of long GRB afterglows 2 hours after the burst onset. Coupled with the rapid response mode available at VLT, allowing reaction times of just a few minutes, X-shooter constitutes an important leap forward on medium resolution spectroscopic studies of GRBs, their host galaxies and intervening systems, probing the early history of the Universe.

astro-ph.HE↗

arXiv2009

The baryonic content and Tully-Fisher relation at z~0.6

[abr.] Using the multi-integral-field spectrograph GIRAFFE at VLT, we previsouly derived the stellar-mass Tully-Fisher Relation (smTFR) at z~0.6, and found that the distant relation is systematically offset by roughly a factor of two toward lower masses. We extend the study of the evolution of the TFR by establishing the first distant baryonic TFR. To derive gas masses in distant galaxies, we estimate a gas radius and invert the Schmidt-Kennicutt law between star formation rate and gas surface densities. We find that gas extends farther out than the UV light from young stars, a median of ~30%. We present the first baryonic TFR (bTFR) ever established at intermediate redshift and show that, within an uncertainty of +/-0.08 dex, the zeropoint of the bTFR does not appear to evolve between z~0.6 and z=0. The absence of evolution in the bTFR over the past 6 Gyr implies that no external gas accretion is required for distant rotating disks to sustain star formation until z=0 and convert most of their gas into stars. Finally, we confirm that the larger scatter found in the distant smTFR, and hence in the bTFR, is caused entirely by major mergers. This scatter results from a transfer of energy from bulk motions in the progenitors, to random motions in the remnants, generated by shocks during the merging. Shocks occurring during these events naturally explain the large extent of ionized gas found out to the UV radius in z~0.6 galaxies. All the results presented in this paper support the ``spiral rebuilding scenario'' of Hammer and collaborators, i.e., that a large fraction of local spiral disks have been reprocessed during major mergers in the past 8 Gyr.

astro-ph.CO↗

arXiv2009

The formation of disks in massive spiral galaxies

The flatness of the rotation curve inside spiral galaxies is interpreted as the imprint of a halo of invisible matter. Using the deepest observations of distant galaxies, we have investigated how large disks could have been formed. Observations include spatially resolved kinematics, detailed morphologies and photometry from UV to mid-IR. Six Giga-years ago, half of the present-day spirals had anomalous kinematics and morphologies that considerably affect the scatter of the Tully Fisher relation. All anomalous galaxies can be modelled through gas-rich, major mergers that lead to a rebuilt of a new disk. The spiral-rebuilding scenario is proposed as a new channel to form large disks in present-day spirals and it accounts for all the observed evolutions since the last 6 Giga-years. A large fraction of the star formation is linked to merging events during their whole durations.

astro-ph.CO↗

arXiv2009

The Hubble sequence: just a vestige of merger events?

Abr: We investigate whether the Hubble sequence can be reproduced by the relics of merger events. We verify that, at zmed=0.65, the abundant population of anomalous starbursts is mainly linked to the local spirals. Their morphologies are dominated by young stars and are related to their ionised-gas kinematics. We show that both morphologies and kinematics can be reproduced by using gas modelling from Barnes' (2002) study of major mergers. Using our modelling to estimate the gas-to-stars transformation during a merger, we identify the gas fraction in the progenitors to be generally above 50%. All distant and massive starbursts can be distributed along a temporal sequence from the first passage to the nuclei fusion and then to the disk rebuilding phase. It confirms that the rebuilding spiral disk scenario is possibly an important channel for the formation of present-day disks in spirals. Because half of the present-day spirals had peculiar morphologies and anomalous kinematics at zmed=0.65, they could indeed be in major mergers phases 6 Gyrs ago, and almost all at z~1. It is time now to study in detail the formation of spiral disks and of their substructures, including bulge, disks, arms, bars, rings that may mainly originate from instabilities created during the last major merger.

astro-ph.CO↗

arXiv2009

The physics of galaxy evolution with EAGLE

One of the prominent science goal of the ELTs will be to study the physics and mass assembly of galaxies at very high redshifts. Here, we present the galaxy evolution science case for EAGLE, which is a NIR multi-integral field spectrograph for the E-ELT currently under phase A study. We summarize results of simulations conducted to derive high-level requirements. In particular, we show how we have derived the specifications for the ensquared energy that the AO system needs to provide to reach the scientific goals of the instrument. Finally, we present future strategies to conduct galaxy surveys with EAGLE.

astro-ph.IM↗

arXiv2009

A surviving disk from a galaxy collision at z=0.4

Spiral galaxies dominate the local galaxy population. Disks are known to be fragile with respect to collisions. Thus it is worthwhile to probe under which conditions a disk can possibly survive such interactions. We present a detailed morpho-kinematics study of a massive galaxy with two nuclei, J033210.76--274234.6, at z=0.4. The morphological analysis reveals that the object consists of two bulges and a massive disk, as well as a faint blue ring. Combining the kinematics with morphology we propose a near-center collision model to interpret the object. We find that the massive disk is likely to have survived the collision of galaxies with an initial mass ratio of ~4:1. The N-body/SPH simulations show that the collision possibly is a single-shot polar collision with a very small pericentric distance of ~1 kpc and that the remnant of the main galaxy will be dominated by a disk. The results support the disk survival hypothesis. The survival of the disk is related to the polar collision with an extremely small pericentric distance. With the help of N-body/SPH simulations we find the probability of disk survival is quite large regardless whether the two galaxies merge or not.

astro-ph.GA↗

arXiv2009

A forming, dust enshrouded disk at z=0.43: the first example of a late type disk rebuilt after a major merger?

Abreg: By combining HST/UDF imagery with kinematics from VLT/GIRAFFE we derive a physical model of distant galaxy J033245.11-274724.0 in a way similar to what can be done in the nearby Universe. Here we study the properties of a distant compact LIRGs galaxy. Given the photometric and spectro photometric accuracies, we can decompose the galaxy in sub components and correct them for reddening. The galaxy is dominated by a dust enshrouded disk revealed by UDF imagery. The disk radius is half that of the Milky Way and the galaxy have a SFR=20Mo/yr. Morphology and kinematics show that gas and stars together spiral inwards rapidly to feed the disk and the central regions. A combined system of a bar and two non rotating spiral arms regulates the material accretion, induces large sigma, with sigma larger than 100 km/s and redistributes the angular momentum (AM). The detailed physical properties resemble to the expectations from modeling a merger of two equal mass, gaseous rich galaxies, 0.5 Gyr after the merger. In its later evolution, this galaxy could become a late type galaxy which falls on the T-F relation, with an AM mostly induced by the orbital AM of the merger.

astro-ph.GA↗

arXiv2008

A forming disk at z~0.6: Collapse of a gaseous disk or major merger remnant?

[Abridged] We present and analyze observations of J033241.88-274853.9 at z=0.6679, using multi-wavelength photometry and imaging with FLAMES/GIRAFFE 3D spectroscopy. J033241.88-274853.9 is found to be a blue, young (~320Myr) stellar disk embedded in a very gas-rich (fgas=73-82% with log(Mstellar/Mo)=9.45) and turbulent phase that is found to be rotating on large spatial scales. We identified two unusual properties of J033241.88-274853.9. (1) The spatial distributions of the ionized gaseous and young stars show a strong decoupling; while almost no stars can be detected in the southern part down to the very deep detection limit of ACS/UDF images, significant emission from the [OII] ionized gas is detected. (2) We detect an excess of velocity dispersion in the southern part of J033241.88-274853.9 in comparison to expectations from a rotating disk model. We considered two disk formation scenarios, depending on the gaseous phase geometry. In the first one, we examined whether J033241.88-274853.9 could be a young rotating disk that has been recently collapsed from a pre-existing, very gas-rich rotating disk. This scenario requires two (unknown) additional assumptions to explain the decoupling between the distribution of stars and gas and the excess of velocity dispersion in the same region. In a second scenario, we examine whether J033241.88-274853.9 could be a merger remnant of two gas-rich disks. In this case, the asymmetry observed between the gas and star distributions, as well as the excess of velocity dispersion, find a common explanation. Shocks produced during the merger in this region can be ionized easily and heat the gas while preventing star formation. This makes this scenario more satisfactory than the collapse of a pre-existing, gas-rich rotating disk.

astro-ph↗

arXiv2008

Images IV: Strong evolution of the oxygen abundance in gaseous phases of intermediate mass galaxies since z=0.8

Intermediate mass galaxies (logM(Msun)>10) at z~0.6 are the likeliest progenitors of the present-day numerous population of spirals. There is growing evidence that they have evolved rapidly since the last 6 to 8 Gyr ago, and likely have formed a significant fraction of their stellar mass, often showing perturbed morphologies and kinematics. We have gathered a representative sample of 88 such galaxies and have provided robust estimates of their gas phase metallicity. For doing so, we have used moderate spectral resolution spectroscopy at VLT/FORS2 with unprecedented high S/N allowing to remove biases coming from interstellar absorption lines and extinction to establish robust values of R23=([OII]3727 + [OIII]4959,5007)/Hbeta. We definitively confirm that the predominant population of z~0.6 starbursts and luminous IR galaxies (LIRGs) are on average, two times less metal rich than the local galaxies at a given stellar mass. We do find that the metal abundance of the gaseous phase of galaxies is evolving linearly with time, from z=1 to z=0 and after comparing with other studies, from z=3 to z=0. Combining our results with the reported evolution of the Tully Fisher relation, we do find that such an evolution requires that ~30% of the stellar mass of local galaxies have been formed through an external supply of gas, thus excluding the close box model. Distant starbursts & LIRGs have properties (metal abundance, star formation efficiency & morphologies) similar to those of local LIRGs. Their underlying physics is likely dominated by gas infall probably through merging or interactions. Our study further supports the rapid evolution of z~0.4-1 galaxies. Gas exchanges between galaxies is likely the main cause of this evolution.

astro-ph↗

arXiv2008

Coupling MOAO with Integral Field Spectroscopy: specifications for the VLT and the E-ELT

[Abridged] We have developed an end-to-end simulation to specify the science requirements of a MOAO-fed integral field spectrograph on either an 8m or 42m telescope. Our simulations re-scales observations of local galaxies or results from numerical simulations of disk or interacting galaxies. For the current analysis, we limit ourselves to a local disk galaxy which exhibits simple rotation and a simulation of a merger. We have attempted to generalize our results by introducing the simple concepts of "PSF contrast" which is the amount of light polluting adjacent spectra which we find drives the smallest EE at a given spatial scale. The choice of the spatial sampling is driven by the "scale-coupling", i.e., the relationship between the IFU pixel scale and the size of the features that need to be recovered by 3D spectroscopy in order to understand the nature of the galaxy and its substructure. Because the dynamical nature of galaxies are mostly reflected in their large-scale motions, a relatively coarse spatial resolution is enough to distinguish between a rotating disk and a major merger. Although we used a limited number of morpho-kinematic cases, our simulations suggest that, on a 42m telescope, the choice of an IFU pixel scale of 50-75 mas seems to be sufficient. Such a coarse sampling has the benefit of lowering the exposure time to reach a specific signal-to-noise as well as relaxing the performance of the MOAO system. On the other hand, recovering the full 2D-kinematics of z~4 galaxies requires high signal-to-noise and at least an EE of 34% in 150 mas (2 pixels of 75 mas). Finally, we carried out a similar study at z=1.6 with a MOAO-fed spectrograph for an 8m, and find that at least an EE of 30% at 0.25 arcsec spatial sampling is required to understand the nature of disks and mergers.

astro-ph↗

arXiv2008

IMAGES-III: The evolution of the Near-Infrared Tully-Fisher relation over the last 6 Gyr

Using the multi-integral field spectrograph GIRAFFE at VLT, we have derived the K-band Tully-Fisher relation (TFR) at z~0.6 for a representative sample of 65 galaxies with emission lines. We confirm that the scatter in the z~0.6 TFR is caused by galaxies with anomalous kinematics, and find a positive and strong correlation between the complexity of the kinematics and the scatter that they contribute to the TFR. Considering only relaxed-rotating disks, the scatter, and possibly also the slope of the TFR, do not appear to evolve with z. We detect an evolution of the K-band TFR zero point between z~0.6 and z=0, which, if interpreted as an evolution of the K-band luminosity of rotating disks, would imply that a brightening of 0.66+/-0.14 mag occurs between z~0.6 and z=0. Any disagreement with the results of Flores et al. (2006) are attributed to both an improvement of the local TFR and the more detailed accurate measurement of the rotation velocities in the distant sample. Most of the uncertainty can be explained by the relatively coarse spatial-resolution of the kinematical data. Because most rotating disks at z~0.6 are unlikely to experience further merging events, one may assume that their rotational velocity does not evolve dramatically. If true, our result implies that rotating disks observed at z~0.6 are rapidly transforming their gas into stars, to be able to double their stellar masses and be observed on the TFR at z=0. The rotating disks observed are indeed emission-line galaxies that are either starbursts or LIRGs, which implies that they are forming stars at a high rate. Thus, a significant fraction of the rotating disks are forming the bulk of their stars within 6 to 8 Gyr, in good agreement with former studies of the evolution of the M-Z relation.

astro-ph↗

arXiv2008

IMAGES II. A surprisingly low fraction of undisturbed rotating spiral disks at z~0.6: The morpho-kinematical relation 6 Gyrs ago

We present a first combined analysis of the morphological and dynamical properties for the Intermediate MAss Galaxy Evolution Sequence (IMAGES) sample. It is a representative sample of 52 z~0.6 galaxies with Mstell from 1.5 to 15 10^10Msun and possessing 3D resolved kinematics and HST deep imaging in at least two broad band filters. We aim at evaluate robustly the evolution of rotating spirals since z~0.6, as well as to test the different schemes for classifying galaxies morphologically. We used all the information provided by multi-band images, color maps and 2 dimensional light fitting to assign to each object a morphological class. We divided our sample between spiral disks, peculiar objects, compact objects and mergers. Using our morphological classification scheme, 4/5 of identified spirals are rotating disks and more than 4/5 of identified peculiar galaxies show complex kinematics, while automatic classification methods such as Concentration-Asymmetry and GINI-M20 severely overestimate the fraction of relaxed disk galaxies. Using this methodology, we find that the fraction of rotating spirals has increased by a factor ~ 2 during the last 6 Gyrs, a much higher fraction that found previously based on morphologies alone. These rotating spiral disks are forming stars very rapidly, doubling their stellar masses over the last 6 Gyrs, while most of their stars have been formed few Gyrs earlier, which reveals the presence of a large gas supply. Because they are likely the progenitors of local spirals, we can conjecture how their properties are evolving. Their disks show some evidence for an inside-out growth and the gas supply/accretion is not made randomly as the disk need to be stable in order to match the local disk properties.

astro-ph↗

arXiv2007

IMAGES: a unique view of the galaxy mass assembly since z=1

The Large Program IMAGES is near 2/3 of its completion. It provides us with kinematics (GIRAFFE deployable IFUs), gas chemistry (FORS2), detailed morphologies (HST/ACS) and IR photometry (Spitzer) for a set of 70 galaxies representative of intermediate mass galaxies (MJ<=-20.3 or 1.5e10 Mo) at z=0.4-0.75. We discover that, 6 Gyr ago, a significant fraction of galaxies (>40%) had anomalous kinematics, i.e. kinematics significantly discrepant from those of rotational or dispersion supported galaxies. The anomalous kinematics cause the observed large dispersion of the Tully-Fisher relation at large distances. IMAGES will soon allow us to study distant galaxies at a level of detail almost comparable to that of nearby galaxies.

astro-ph↗

arXiv2007

The MW is an exceptionnally quiet galaxy: implications for spiral formation

We compare both the Milky Way and M31 to local external disk galaxies within the same mass range, using their relative locations in the planes formed by Vflat vs. MK (the Tully-Fisher relation), j_disk (specific angular momentum) and the average Fe abundance of stars in the galaxy outskirts. We find, for all relationships, that the MW is systematically offset by 1 sigma or more, showing a significant deficiency in stellar mass, angular momentum, disk radius and [Fe/H] in the stars in its outskirts at a given Vflat. Our Galaxy appears to have escaped any significant merger over the last 10-11 Gyr which may explain its peculiar properties. As with M31, most local spirals show evidence for a history shaped mainly by relatively recent merging.

astro-ph↗

arXiv2007

IMAGES I. Strong evolution of galaxy kinematics since z=1

(abbreviated) We present the first results of the ESO large program, ``IMAGES'' which aims at obtaining robust measurements of the kinematics of distant galaxies using the multi-IFU mode of GIRAFFE on the VLT. 3D spectroscopy is essential to robustly measure the often distorted kinematics of distant galaxies (e.g., Flores et al. 2006). We derive the velocity fields and $σ$-maps of 36 galaxies at 0.4 15 A) at z=0.4-0.75, which are a representative subsample of the population of M_stellar>1.5x10^{10} M_sun emission line galaxies in this redshift range, and are largely unaffected by cosmic variance. Taking into account all galaxies -with or without emission lines- in that redshift range, we find that at least 41+/-7% of them have anomalous kinematics, i.e., they are not dynamically relaxed. This includes 26+/-7% of distant galaxies with complex kinematics, i.e., they are not simply pressure or rotationally supported. Our result implies that galaxy kinematics are among the most rapidly evolving properties, because locally, only a few percent of the galaxies in this mass range have complex kinematics.

astro-ph↗

arXiv2007

First detection of a minor merger a z~0.6

Numerical simulations predict that minor mergers are an important channel for the mass assembly of galaxies. However, minor mergers are relatively difficult to detect using imaging, especially at high redshift. While such events are much less violent than major mergers, they can nevertheless leave several features on the kinematical structures of remnant galaxies which could be detected using 3D spectroscopy. We present the first direct detection of a minor merger in a z~0.6 galaxy. Such events could indeed be good candidates to explain the kinematics of perturbed rotating disks observed with GIRAFFE at z~0.6. We present photometric and kinematical evidence of such an event in a combined analysis of three-band HST/ACS imaging and VLT/GIRAFFE 2D-kinematics. Using these data, we are able to demonstrate that a minor merger of a relatively small satellite (mass ratio ~1:18) is occurring in this galaxy. We also derive a total SFR ~21Mo/yr. Minor mergers could be one of the physical processes explaining the kinematics of perturbed rotating disks, which represent ~25% of emission line intermediate mass galaxies at z~0.6. 3D spectroscopy appears to be a very good tool to identify minor mergers in distant (and local) galaxies.

astro-ph↗