arXiv subjects

C. Munoz-Tunon

Publications and source records attributed to C. Munoz-Tunon.

At least 37 records · Page 2Linked to original sources

arXiv2010

Atmosphere Extinction at the ORM on La Palma: A 20 yr Statistical Database Gathered at the Carlsberg Meridian Telescope

The Observatorio del Roque de los Muchachos (ORM), in the Canary Islands (Spain), was one of the candidates to host the future European Extremely Large Telescope (E-ELT) and is the site of the Gran Telescopio Canarias (GTC), the largest optical infrared facility to date. Sky transparency is a key parameter as it defines the quality of the photometry to be acquired in the astronomical observations. We present a study of the atmosphere extinction at the ORM, carried out after analysis of a database spanning more than 20 yr, to our knowledge, the longest and most complete and homogeneous in situ database available for any observatory. It is based on photometric measurements in the V band and r' band (transformed to the V -band extinction coefficient kV) using the Carlsberg Meridian Telescope (CMT). Clear seasonal variations that repeat yearly are observed. The median value of kV is 0.13 mag/airmass; the mean value has a maximum in the summer months (June- September), corresponding to the season with maximum frequency of nights affected by dust or cirrus (~29% in summer, but only ~13% during the rest of the year). Two volcanic eruptions took place during the database baseline, which has enabled the study of the impact of volcanoes on the global atmosphere extinction. For the 5 yr of available information, we have estimated the average monthly weather downtime from the CMT data log, obtaining a result (20.7%) in reasonable agreement with earlier studies. The main conclusion of our study is that there is no significant evidence from the CMT data for any secular changes in kV over the 20 yr database baseline.

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arXiv2010

A study of the interplay between ionized gas and star clusters in the central region of NGC 5253 with 2D spectroscopy

ABRIDGED: A detailed 2D study of the central region of NGC5253 has been performed to characterize the stellar and ionized gas structure as well as the extinction distribution, physical properties and kinematics of the ionized gas in the central ~210pc x 130pc. We utilized optical integral field spectroscopy (IFS) data obtained with FLAMES. A detailed extinction map for the ionized gas in NGC5253 shows that the largest extinction is associated with the prominent Giant HII region. There is an offset of ~0.5" between the peak of the optical continuum and the extinction peak in agreement with findings in the infrared. We found that stars suffer less extinction than gas by a factor of 0.33. The [SII]l6717/[SII]l6731 map shows an electron density (N_e) gradient declining from the peak of emission in Ha (790cm^-3) outwards, while the argon line ratio traces areas with $N_e~4200 - 6200cm^(-3). The area polluted with extra nitrogen, as deduced from the excess [NII]/Ha, extends up to distances of 3.3" (~60pc) from the maximum pollution, which is offset by ~1.5" from the peak of continuum emission. Wolf-Rayet features are distributed in an irregular pattern over a larger area (~100pc x 100pc) and associated with young stellar clusters. We measured He^+ abundances over most of the field of view and values of He^++/H^+<~0.0005 in localized areas which do not coincide, in general, with the areas presenting W-R emission or extra nitrogen. The line profiles are complex. Up to three emission components were needed to reproduce them. One of them, associated with the giant HII region, presents supersonic widths and [NII] and [SII] emission lines shifted up to 40km/s with respect to Ha. Similarly, one of the narrow components presents offsets in the [NII] line of <~20km/s. This is the first time that maps with such velocity offsets for a starburst galaxy have been presented.

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arXiv2010

Automatic unsupervised classification of all SDSS/DR7 galaxy spectra

Using the 'k-means' cluster analysis algorithm, we carry out an unsupervised classification of all galaxy spectra in the seventh and final Sloan Digital Sky Survey data release (SDSS/DR7). Except for the shift to restframe wavelengths, and the normalization to the g-band flux, no manipulation is applied to the original spectra. The algorithm guarantees that galaxies with similar spectra belong to the same class. We find that 99 % of the galaxies can be assigned to only 17 major classes, with 11 additional minor classes including the remaining 1%. The classification is not unique since many galaxies appear in between classes, however, our rendering of the algorithm overcomes this weakness with a tool to identify borderline galaxies. Each class is characterized by a template spectrum, which is the average of all the spectra of the galaxies in the class. These low noise template spectra vary smoothly and continuously along a sequence labeled from 0 to 27, from the reddest class to the bluest class. Our Automatic Spectroscopic K-means-based (ASK) classification separates galaxies in colors, with classes characteristic of the red sequence, the blue cloud, as well as the green valley. When red sequence galaxies and green valley galaxies present emission lines, they are characteristic of AGN activity. Blue galaxy classes have emission lines corresponding to star formation regions. We find the expected correlation between spectroscopic class and Hubble type, but this relationship exhibits a high intrinsic scatter. Several potential uses of the ASK classification are identified and sketched, including fast determination of physical properties by interpolation, classes as templates in redshift determinations, and target selection in follow-up works (we find classes of Seyfert galaxies, green valley galaxies, as well as a significant number of outliers). The ASK classification is publicly accessible through various websites.

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arXiv2010

On the extreme positive star-formation feedback condition in SCUBA sources

We present a detailed study of the hydrodynamics of the matter reinserted by massive stars via stellar winds and supernovae explosions in young assembling galaxies. We show that the interplay between the thermalization of the kinetic energy provided by massive stars, radiative cooling of the thermalized plasma and the gravitational pull of the host galaxy, lead to three different hydrodynamic regimes. These are: a) The quasi-adiabatic supergalactic winds. b) The bimodal flows, with mass accumulation in the central zones and gas expulsion from the outer zones of the assembling galaxy. c) The gravitationally bound regime, for which all of the gas returned by massive stars remains bound to the host galaxy and is likely to be reprocessed into futher generations of stars. Which of the three possible solutions takes place, depends on the mass of the star forming region its mechanical luminosity (or star formation rate) and its size. The model predicts that massive assembling galaxies with large star formation rates similar to those detected in SCUBA sources ($\sim 1000$ M$_\odot$ yr$^{-1}$) are likely to evolve in a positive star-formation feedback condition, either in the bimodal, or in the gravitationally bound regime. This implies that star formation in these sources may have little impact on the intergalactic medium and result instead into a fast interstellar matter enrichment, as observed in high redshift quasars.

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arXiv2009

Supersonic Line Broadening within Young and Massive Super Star Clusters

The origin of supersonic infrared and radio recombination nebular lines often detected in young and massive superstar clusters are discussed. We suggest that these arise from a collection of repressurizing shocks (RSs), acting effectively to re-establish pressure balance within the cluster volume and from the cluster wind which leads to an even broader although much weaker component. The supersonic lines are here shown to occur in clusters that undergo a bimodal hydrodynamic solution (Tenorio-Tagle et al. 2007), that is within clusters that are above the threshold line in the mechanical luminosity or cluster mass vs the size of the cluster (Silich et al. 2004). The plethora of repressurizing shocks is due to frequent and recurrent thermal instabilities that take place within the matter reinserted by stellar winds and supernovae. We show that the maximum speed of the RSs and of the cluster wind, are both functions of the temperature reached at the stagnation radius. This temperature depends only on the cluster heating efficiency ($η$). Based on our two dimensional simulations (Wunsch et al. 2008) we calculate the line profiles that result from several models and confirm our analytical predictions. From a comparison between the predicted and observed values of the half-width zero intensity of the two line components we conclude that the thermalization efficiency in SSC's above the threshold line must be lower than 20%.

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arXiv2009

Search for blue compact dwarf galaxies during quiescence II: metallicities of gas and stars, ages, and star-formation rates

We examine the metallicity and age of a large set of SDSS/DR6 galaxies that may be Blue Compact Dwarf (BCD) galaxies during quiescence (QBCDs).The individual spectra are first classified and then averaged to reduce noise. The metallicity inferred from emission lines (tracing ionized gas) exceeds by ~0.35 dex the metallicity inferred from absorption lines (tracing stars). Such a small difference is significant according to our error budget estimate. The same procedure was applied to a reference sample of BCDs, and in this case the two metallicities agree, being also consistent with the stellar metallicity in QBCDs. Chemical evolution models indicate that the gas metallicity of QBCDs is too high to be representative of the galaxy as a whole, but it can represent a small fraction of the galactic gas, self enriched by previous starbursts. The luminosity weighted stellar age of QBCDs spans the whole range between 1 and 10 Gyr, whereas it is always smaller than 1 Gyr for BCDs. Our stellar ages and metallicities rely on a single stellar population spectrum fitting procedure, which we have specifically developed for this work using the stellar library MILES.

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arXiv2008

Search for Blue Compact Dwarf Galaxies During Quiescence

Blue Compact Dwarf (BCD) galaxies are metal poor systems going through a major starburst that cannot last for long. We have identified galaxies which may be BCDs during quiescence (QBCD), i.e., before the characteristic starburst sets in or when it has faded away. These QBCD galaxies are assumed to be like the BCD host galaxies. The SDSS/DR6 database provides ~21500 QBCD candidates. We also select from SDSS/DR6 a complete sample of BCD galaxies to serve as reference. The properties of these two galaxy sets have been computed and compared. The QBCD candidates are thirty times more abundant than the BCDs, with their luminosity functions being very similar except for the scaling factor, and the expected luminosity dimming associated with the end of the starburst. QBCDs are redder than BCDs, and they have larger HII region based oxygen abundance. QBCDs also have lower surface brightness. The BCD candidates turn out to be the QBCD candidates with the largest specific star formation rate (actually, with the largest H_alpha equivalent width). One out of each three dwarf galaxies in the local universe may be a QBCD. The properties of the selected BCDs and QBCDs are consistent with a single sequence in galactic evolution, with the quiescent phase lasting thirty times longer than the starburst phase. The resulting time-averaged star formation rate is low enough to allow this cadence of BCD -- QBCD phases during the Hubble time.

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arXiv2007

Ionized and neutral gas in the peculiar star/cluster complex in NGC 6946

The characteristics of ionized and HI gas in the peculiar star/cluster complex in NGC 6946, obtained with the 6-m telescope (BTA) SAO RAS, the Gemini North telescope, and the Westerbork Synthesis Radio Telescope (WSRT), are presented. The complex is unusual as hosting a super star cluster, the most massive known in an apparently non-interacting giant galaxy. It contains a number of smaller clusters and is bordered by a sharp C-shaped rim. We found that the complex is additionally unusual in having peculiar gas kinematics. The velocity field of the ionized gas reveals a deep oval minimum, ~300 pc in size, centered 7" east of the supercluster. The Vr of the ionized gas in the dip center is 100 km/s lower than in its surroundings, and emission lines within the dip appear to be shock excited. This dip is near the center of an HI hole and a semi-ring of HII regions. The HI (and less certainly, HII) velocity fields reveal expansion, with the velocity reaching ~30 km/s at a distance about 300 pc from the center of expansion, which is near the deep minimum position. The super star cluster is at the western rim of the minimum. The sharp western rim of the whole complex is plausibly a manifestation of a regular dust arc along the complex edge. Different hypotheses about the complex and the Vr depression origins are discussed, including a HVC/dark mini-halo impact, a BCD galaxy merging, and a gas outflow due to release of energy from the supercluster stars.

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arXiv2007

A Study of Catalogued Nearby Galaxy Clusters in the SDSS-DR4: I. Cluster Global Properties

We have selected a sample of 88 nearby (z<0.1) galaxy clusters from the SDSS-DR4 with redshift information for the cluster members. We have derived global properties for each cluster, such as their mean recessional velocity, velocity dispersion, and virial radii. Cluster galaxies have been grouped in two families according to their $u-r$ colours. The total sample consists of 10865 galaxies. As expected, the highest fraction of galaxies (62%) turned to be early-type (red) ones, being located at smaller distances from the cluster centre and showing lower velocity dispersions than late-type (blue) ones. The brightest cluster galaxies are located in the innermost regions and show the smallest velocity dispersions. Early-type galaxies also show constant velocity dispersion profiles inside the virial radius and a mild decline in the outermost regions. In contrast, late-type galaxies show always decreasing velocity dispersions profiles. No correlation has been found between the fraction of blue galaxies and cluster global properties, such as cluster velocity dispersion and galaxy concentration. In contrast, we found correlation between the X-ray luminosity and the fraction of blue galaxies. These results indicate that early- and late-type galaxies may have had different evolution. Thus, blue galaxies are located in more anisotropic and radial orbits than early-type ones. Their star formation seems to be independent of the cluster global properties in low mass clusters, but not for the most massive ones. These observational results suggest that the global environment could be important for driving the evolution of galaxies in the most massive cluster ($σ> 800$ km s$^{-1}$). However, the local environment could play a key role in galaxy evolution for low mass clusters.

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arXiv2006

Super Massive Star Clusters: From Superwinds to a Cooling Catastrophe and the Re-processing of the Injected Gas

Different hydrodynamic regimes for the gaseous outflows generated by multiple supernovae explosions and stellar winds occurring within compact and massive star clusters are discussed. It is shown that there exists the threshold energy that separates clusters whose outflows evolve in the quasi-adiabatic or radiative regime from those within which catastrophic cooling and a positive feedback star-forming mode sets in. The role of the surrounding ISM and the observational appearance of the star cluster winds evolving in different hydrodynamic regimes are also discussed.

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arXiv2006

On the structure of giant HII regions and HII galaxies

We review the structural properties of giant extragalactic HII regions and HII galaxies based on two dimensional hydrodynamic calculations, and propose an evolutionary sequence that accounts for their observed detailed structure. The model assumes a massive and young stellar cluster surrounded by a large collection of clouds. These are thus exposed to the most important star-formation feedback mechanisms: photoionization and the cluster wind. The models show how the two feedback mechanisms compete with each other in the disruption of clouds and lead to two different hydrodynamic solutions: The storage of clouds into a long lasting ragged shell that inhibits the expansion of the thermalized wind, and the steady filtering of the shocked wind gas through channels carved within the cloud stratum that results into the creation of large-scale superbubbles. Both solutions are here claimed to be concurrently at work in giant HII regions and HII galaxies, causing their detailed inner structure. A full description of the calculations can be found in The Astrophysical Journal 643, 186. Animated version of the models presented can be found at http://www.iaa.csic.es/\~{}eperez/ssc/ssc.html.

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arXiv2006

On the feedback from super stellar clusters. I. The structure of giant HII regions and HII galaxies

We review the structural properties of giant extragalactic HII regions and HII galaxies based on 2D hydrodynamic calculations, and propose an evolutionary sequence that accounts for their observed detailed structure. The model assumes a massive and young stellar cluster surrounded by a large collection of clouds. These are thus exposed to the most important star-formation feedback mechanisms: photoionization and the cluster wind. The models show how the two feedback mechanisms compete in the disruption of clouds and lead to two different hydrodynamic solutions: The storage of clouds into a long lasting ragged shell that inhibits the expansion of the thermalized wind, and the steady filtering of the shocked wind gas through channels carved within the cloud stratum. Both solutions are claimed to be concurrently at work in giant HII regions and HII galaxies, causing their detailed inner structure. This includes multiple large-scale shells, filled with an X-ray emitting gas, that evolve to finally merge with each other, giving the appearance of shells within shells. The models also show how the inner filamentary structure of the giant superbubbles is largely enhanced with matter ablated from clouds and how cloud ablation proceeds within the original cloud stratum. The calculations point at the initial contrast density between the cloud and the intercloud media as the factor that defines which of the two feedback mechanisms becomes dominant throughout the evolution. Animated version of the models can be found at http://www.iaa.csic.es/\~{}eperez/ssc/ssc.html.

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arXiv2004

Astronomical Site Ranking Based on Tropospheric Wind Statistics

We present comprehensive and reliable statistics of high altitude wind speeds and the tropospheric flows at the location of five important astronomical observatories. Statistical analysis exclusively of high altitude winds point to La Palma as the most suitable site for adaptive optics, with a mean value of 22.13 m/s at the 200 mbar pressure level. La Silla is at the bottom of the ranking, with the largest average value 200 mbar wind speed(33.35 m/s). We have found a clear annual periodicity of high altitude winds for the five sites in study. We have also explored the connection of high to low altitude atmospheric winds as a first approach of the linear relationship between the average velocity of the turbulence and high altitude winds (Sarazin & Tokovinin 2001). We may conclude that high and low altitude winds show good linear relationships at the five selected sites. The highest correlation coefficients correspond to Paranal and San Pedro Martir, while La Palma and La Silla show similar high to low altitude wind connection. Mauna Kea shows the smallest degree of correlation, which suggests a weaker linear relationship. Our results support the idea of high altitude winds as a parameter for rank astronomical sites in terms of their suitability for adaptive optics, although we have no evidence for adopting the same linear coefficient at different sites. The final value of this linear coefficient at a particular site could drastically change the interpretation of high altitude wind speeds as a direct parameter for site characterization.

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arXiv2003

Supergalactic winds driven by multiple superstar clusters

We present two dimensional hydrodynamic calculations of free expanding supergalactic winds, taking into consideration strong radiative cooling. Our main premise is that supergalactic winds are powered by collections of superstar clusters. Every individual superstar cluster is a source of a high metallicity radiative supersonic outflow (paper I, 2003, ApJ, 590, 791). The interaction of winds from neighboring knots of star formation is shown to lead to a collection of stationary oblique shocks and crossing shocks, able to structure the general outflow into a network of dense and cold, kpc long filaments that originate near the base of the outflow. The shocks also lead to extended regions of diffuse soft X-ray emission and furthermore, to channel the outflow with a high degree of collimation into the intergalactic medium.

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arXiv2003

Deep Near Infrared Mapping of Young and Old Stars in Blue Compact Dwarf Galaxies

We analyze J, H and Ks near-infrared data for 9 Blue Compact Dwarf (BCD) galaxies, selected from a larger sample that we have already studied in the optical. We present contour maps, surface brightness and color profiles, as well as color maps of the sample galaxies. The morphology of the BCDs in the NIR has been found to be basically the same as in the optical. The inner regions of these systems are dominated by the starburst component. At low surface brightness levels the emission is due to the underlying host galaxy; the latter is characterized by red, radially constant colors and isophotes well fit by ellipses. We derive accurate optical near--infrared host galaxy colors for eight of the sample galaxies; these colors are typical of an evolved stellar population. Interestingly, optical near--infrared color maps reveal the presence of a complex, large-scale absorption pattern in three of the sample galaxies. We study the applicability of the Sersic law to describe the surface brightness profiles of the underlying host galaxy, and find that, because of the limited surface brightness interval over which the fit can be made, the derived Sersic parameters are very sensitive to the selected radial interval and to errors in the sky subtraction. Fitting an exponential model gives generally more stable results, and can provide a useful tool to quantify the structural properties of the host galaxy and compare them with those of other dwarf classes as well as with those of star-forming dwarfs at higher redshifts.

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arXiv2003

On the rapidly cooling interior of supergalactic winds

The steady state numerical solution and two dimensional hydrodynamic calculations of supergalactic winds generated by super star clusters are presented. Two possible regimes: quasi-adiabatic and strongly radiative are thoroughly discussed. It is shown that superwinds driven by compact and powerful starbursts undergo catastrophic cooling close to their sources, and establish a temperature distribution radically different from those obtained in the adiabatic solution. At the same time, both velocity and density radial distributions remain almost unchanged given the speed of the rapidly diverging flow. The rapid fall in temperature as a function of radius reduces the size of the zone radiating in X-rays and decreases the superwind X-ray luminosity. At the same time, cooling brings the 10$^4$ K boundary closer to the wind center, and promotes the establishment of an extended ionized fast moving envelope. This should show up as a weak and broad ($\sim 1000$ km s$^{-1}$) line emission component at the base of the much narrower line caused by the central HII region.

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arXiv2003

Superbubbles vs Super-galactic winds

We stress some of the major differences between supergalactic winds and giant superbubbles evolving into the giant low density haloes of galaxies. We review major properties of bursts of star formation and the critical energy required for mass ejection both in the case of an ISM strongly flattened by rotation and that imposed by a more extended ISM distribution arising from a smaller rotation. The limits are thus establish for galaxies with an ISM mass in the range 10$^6$ M$_\odot$ to more than 10$^9$ M$_\odot$, and are compared with a sample of local galaxies. Some of these galaxies seem to be above the critical limit despite the fact that their structure is clearly that of a superbubble. True supergalactic winds, as evidence by M82, are shown to exceed the critical limit by more than an order of magnitude and thus the limit derived by Silich & Tenorio-Tagle (2001) for mass ejection should be regarded as a lower limit.

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arXiv2003

Dwarfs after Mergers? The case of NGC520, NGC772, Arp141, NGC3226/7, NGC3656 and Arp299

We present results from a survey of dwarf galaxy candidates in the vicinity of strongly interacting galaxies. The goal of the survey was a test of the hypothesis that massive condensations of stars and HI in tidal tails of large interacting galaxies may be a significant source of independent, self-gravitating dwarf galaxies. These so called tidal dwarf galaxies (TDG) can be expected to resemble the blue luminous knots found in tidal tails, but also might appear as redder, evolved systems if formed much before they are being observed. For the present study, a homogeneous subsample of 6 fields was selected from the catalog of extended objects in fields around 15 strongly interacting galaxies by Deeg et al. (1998). Criteria for the subsample were: similar redshifts of the central interacting galaxies, and photometric completeness of the extended objects in V and R. The number density of these TDG candidates was compared with expected background galaxy densities. Within the statistical errors, background galaxies account for most, if not all of the extended objects. There is no evidence for a substantial locally formed dwarf galaxy population. Thus, we conclude that field galaxy-galaxy interactions are likely to result in the formation of only a few long-lived TDG.

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