arXiv subjects

Santiago Arribas

Publications and source records attributed to Santiago Arribas.

At least 145 records · Page 8Linked to original sources

arXiv2016

Velocities of warm galactic outflows from synthetic Hα observations of star-forming galaxies

The velocity structure imprinted in the Hα emission line profiles contains valuable information about galactic outflows. Using a set of high-resolution zoom-in cosmological simulations of galaxies at z=2, we generate Hα emission line profiles, taking into account the temperature-dependent Hα emissivity, as well as dust extinction. The Hα line can be described as a sum of two gaussians, as typically done with observations. In general, its properties are in good agreement with those observed in local isolated galaxies with similar masses and star formation rates, assuming a spatially constant clumping factor of c=24. Blueshifted outflows are very common in the sample. They extend several kpc above the galaxy discs. They are also spread over the full extent of the discs. However, at small radii, the material with high velocities tends to remain confined within a thick disc, as part of galactic fountains or a turbulent medium, most probably due to the deeper gravitational potential at the galaxy centre.

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arXiv2016

Ionized outflows in luminous type 2 AGNs at z<0.6: no evidence for significant impact on the host galaxies

We investigate the presence of extended ionized outflows in 18 luminous type 2 AGNs (11 quasars and 7 high luminosity Seyfert 2s) at 0.3 =severalx100 pc and upper limits R<1-2 kpc. Our results are inconsistent with related studies which suggest that large scale R~several-15 kpc are ubiquitous in QSO2. We study the possible causes of discrepancy and propose that seeing smearing is the cause of the large inferred sizes. The implications in our understanding of the feedback phenomenon are important since the mass M (through the density), mass injection M(dot) and energy injection rates E(dot) of the outflows become highly uncertain. One conclusion seems unavoidable: M, M(dot), E(dot) are modest or low compared with previous estimations. No evidence is found supporting that typical outflows can affect the interstellar medium of the host galaxies accross spatial scales >~1-2 kpc.

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arXiv2016

VLT-SINFONI sub-kpc study of the star formation in local LIRGs and ULIRGs: Analysis of the global $Σ_{\rm SFR}$ structure and characterisation of individual star-forming clumps

We present a 2D study of star formation at kpc and sub-kpc scales of a sample of local (z<0.1) U/LIRGs, based on near-IR VLT-SINFONI observations. We obtained integrated measurements of the star formation rate (SFR) and star formation rate surface density, together with their 2D distributions, based on Br_gamma and Pa_alpha emission. We observe a tight linear correlation between the SFR derived from our extinction-corrected measurements and that derived from 24 micron data, and a reasonable agreement with SFR derived from total IR luminosity. Our near-IR measurements are on average a factor 3 larger than optical SFR, even when extinction corrections are applied. We found that LIRGs have a median-observed star formation rate surface density of 1.72 Msun/yr/kpc^2 for the extinction-corrected distribution, whilst ULIRGs have 0.23 Msun/yr/kpc^2, respectively. These median values for ULIRGs increase up to 2.90 Msun/yr/kpc^2, when only their inner regions, covering the same size as the average FoV of LIRGs, are considered. We identified a total of 95 individual SF clumps in our sample, with sizes within 60-1500pc, and extinction-corrected Pa_alpha luminosities of 10^5-10^8 Lsun. Star-forming clumps in LIRGs are about ten times larger and thousands of times more luminous than typical clumps in spiral galaxies. Clumps in ULIRGs have sizes similar (x0.5-1) to those of high-z clumps, having Pa_alpha luminosities similar to some high-z clumps, and about 10 times less luminous than the most luminous high-z clumps identified so far. We also observed a change in the slope of the L-r relation. A likely explanation is that most luminous galaxies are interacting and merging, and therefore their size represents a combination of the distribution of the star-forming clumps within each galaxy in the system plus the effect of the projected distance.

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arXiv2016

Distinguishing `disks' from `mergers': tracing the kinematic asymmetries in local (U)LIRGs using `kinemetry'-based criteria

The kinematic characterization of different galaxy populations is a key observational input to distinguish between different galaxy evolutionary scenarios, since it helps to determine the number ratio of rotating disks to mergers at different cosmic epochs. Local (U)LIRGs offer a unique opportunity to study at high linear resolution and S/N extreme star forming events and compare them with those observed at high-z. We obtained Very Large Telescope (VLT) VIMOS optical integral field spectroscopy (IFS) data of a sample of 38 (U)LIRGs. The `unweighted' and `weighted' {kinemetry}-based methods are used to kinematically classify our galaxies in `disk' and `merger'. We simulate our systems at z=3 to evaluate how a loss of angular resolution affects our results. From the kinemetry-based analysis we are able classify our local (U)LIRGs in three distinct kinematic groups according to their total kinematic asymmetry values (K$_{tot}$) as derived when using the weighted (unweighted) method: 1) 25 out of 50 galaxies are kinematically classified as `disk', with a K$_{tot}\leq$ 0.16 (0.14); 2) 9 out of 50 galaxies are kinematically classified as `merger', with a K$_{tot}\geq$ 0.94 (0.66); 3) 16 out of 50 galaxies lie in the `transition region', in which disks and mergers coexist, with 0.16 (0.14) $<$ K$_{tot}$ $<$ 0.94 (0.66). When we apply our criteria to the high-z simulated systems, a lower total kinematic asymmetry frontier value (K$_{tot}$ $\sim$ 0.16 ($\sim$ 0.14)) is derived with respect to that found locally. The loss of angular resolution smears out the kinematic features, thus making objects to appear more kinematically regular than actually they are.

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arXiv2015

Understanding the two-dimensional ionization structure in luminous infrared galaxies. A near-IR integral field spectroscopy perspective

We investigate the 2D excitation structure of the ISM in a sample of LIRGs and Seyferts using near-IR IFS. This study extends to the near-IR the well-known optical and mid-IR emission line diagnostics used to classify activity in galaxies. Based on the spatially resolved spectroscopy of prototypes, we identify in the [FeII]1.64/Br$γ$ - H_2 1-0S(1)/Br$γ$ plane regions dominated by the different heating sources, i.e. AGNs, young MS massive stars, and evolved stars i.e. supernovae. The ISM in LIRGs occupy a wide region in the near-IR diagnostic plane from -0.6 to +1.5 and from -1.2 to +0.8 (in log units) for the [FeII]/Br$γ$ and H_2/Br$γ$ line ratios, respectively. The corresponding median(mode) ratios are +0.18(0.16) and +0.02(-0.04). Seyferts show on average larger values by factors ~2.5 and ~1.4 for the [FeII]/Br$γ$ and H_2/Br$γ$ ratios, respectively. New areas and relations in the near-IR diagnostic plane are defined for the compact, high surface brightness regions dominated by AGN, young ionizing stars, and SNe explosions, respectively. In addition, the diffuse regions affected by the AGN radiation field cover an area similar to that of Seyferts, but with high values in [FeII]/Br$γ$ that are not as extreme. The extended, non-AGN diffuse regions cover a wide area in the diagnostic diagram that overlaps that of individual excitation mechanisms (i.e. AGN, young stars, and SNe), but with its mode value to that of the young SF clumps. This indicates that the excitation conditions of the diffuse ISM are likely due to a mixture of the different ionization sources. The integrated line ratios in LIRGs show higher excitation conditions i.e. towards AGNs, than those measured by the spatially resolved spectroscopy. If this behaviour is representative, it would have clear consequences when classifying high-z, SF galaxies based on their near-IR integrated spectra.

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arXiv2015

Star-formation histories of local luminous infrared galaxies

We present the analysis of the integrated spectral energy distribution (SED) from the ultraviolet (UV) to the far-infrared and H$α$ of a sample of 29 local systems and individual galaxies with infrared (IR) luminosities between 10^11 Lsun and 10^11.8 Lsun. We have combined new narrow-band H$α$+[NII] and broad-band g, r optical imaging taken with the Nordic Optical Telescope (NOT), with archival GALEX, 2MASS, Spitzer, and Herschel data. The SEDs (photometry and integrated H$α$ flux) have been fitted with a modified version of the MAGPHYS code using stellar population synthesis models for the UV-near-IR range and thermal emission models for the IR emission taking into account the energy balance between the absorbed and re-emitted radiation. From the SED fits we derive the star-formation histories (SFH) of these galaxies. For nearly half of them the star-formation rate appears to be approximately constant during the last few Gyrs. In the other half, the current star-formation rate seems to be enhanced by a factor of 3-20 with respect to that occured ~1 Gyr ago. Objects with constant SFH tend to be more massive than starbursts and they are compatible with the expected properties of a main-sequence (M-S) galaxy. Likewise, the derived SFHs show that all our objects were M-S galaxies ~1 Gyr ago with stellar masses between 10^10.1 and 10^11.5 Msun. We also derived from our fits the average extinction (A_v=0.6-3 mag) and the polycyclic aromatic hydrocarbons (PAH) luminosity to L(IR) ratio (0.03-0.16). We combined the A_v with the total IR and H$α$ luminosities into a diagram which can be used to identify objects with rapidly changing (increasing or decreasing) SFR during the last 100 Myr.

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arXiv2014

Outflow of hot and cold molecular gas from the obscured secondary nucleus of NGC3256: closing in on feedback physics

The nuclei of merging galaxies are often deeply buried in dense layers of gas and dust. In these regions, gas outflows driven by starburst and AGN activity are believed to play a crucial role in the evolution of these galaxies. However, to fully understand this process it is essential to resolve the morphology and kinematics of such outflows. Using near-IR integral-field spectroscopy obtained with VLT/SINFONI, we detect a kpc-scale structure of high-velocity molecular hydrogen (H2) gas associated with the deeply buried secondary nucleus of the IR-luminous merger NGC3256. We show that this structure is likely the hot component of a molecular outflow, which is detected also in the cold molecular gas by Sakamoto et al. This outflow, with a molecular gas mass of M(H2)~2x10^7 Msun, is among the first to be spatially resolved in both the hot H2 gas with VLT/SINFONI and the cold CO-emitting gas with ALMA. The hot and cold components share a similar morphology and kinematics, with a hot-to-cold molecular gas mass ratio of ~6x10^-5. The high (~100 pc) resolution at which we map the geometry and velocity structure of the hot outflow reveals a biconical morphology with opening angle ~40 deg and gas spread across a FWZI~1200 km/s. Because this collimated outflow is oriented close to the plane of the sky, the molecular gas may reach maximum intrinsic outflow velocities of ~1800 km/s, with an average mass outflow rate of at least ~20 Msun/yr. By modeling the line-ratios of various near-IR H2 transitions, we show that the H2 gas in the outflow is heated through shocks or X-rays to a temperature of ~1900K. The energy needed to drive the outflow is likely provided by a hidden Compton-thick AGN or by the nuclear starburst. We show that the global kinematics of the molecular outflow in NGC3256 mimic those of CO-outflows that have been observed at low spatial resolution in starburst- and active galaxies.

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arXiv2014

Ionized gas outflows and global kinematics of low-z luminous star forming galaxies

We study the kinematic properties of the ambient ionized ISM and ionized gas outflows in a large and representative sample of local luminous and ultraluminous infrared galaxies (U/LIRGs) (58 systems, 75 galaxies), on the basis of integral field spectroscopy (IFS)-based high S/N integrated spectra at galactic and sub-galactic, i.e. star forming (SF) clumps, scales. Ambient ionized gas. The velocity dispersion of the ionized ISM in U/LIRGs ( ~ 70 kms-1) is larger than in lower luminosity local star forming galaxies ( ~ 25 kms-1). While for isolated disc LIRGs star formation appears to sustain turbulence, gravitational energy release associated to interactions and mergers plays an important role driving sigma in the U/LIRG range. We also find that the impact of an AGN in ULIRGs is strong, increasing sigma by a factor 1.5 on average. The observed weak dependency of sigma with SFR surface density for local U/LIRGs is in very good agreement with that measured in some high-z samples. Ionized outflows. The presence of ionized gas outflows in U/LIRGs seems universal based on the detection of a broad, usually blueshifted, Halpha line. AGNs in U/LIRGs are able to generate faster (x2) and more massive (x1.4) ionized gas outflows than pure starbursts. The derived ionized mass loading factors are in general below one, with only a few AGNs above this limit. Only a small fraction of the ionized material from low mass LIRGs (log(Mdyn/Msun) < 10.4) could reach the intergalactic medium, with more massive galaxies retaining the gas. The observed average outflow properties in U/LIRGs are similar to high-z galaxies of comparable SFR. In the bright SF clumps found in LIRGs, ionized gas outflows appear to be very common. For a given SFR surface density, outflows in LIRG clumps would be about one to two orders of magnitude less energetic than those launched by clumps in high-z SF galaxies.

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arXiv2013

VLT/VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies: 2D kinematic properties

We present and discuss the 2D kinematic properties of the ionized gas (Halpha) in a sample of 38 local (ultra) luminous infrared galaxies [(U)LIRGs] (31 LIRGs and 7 ULIRGs) observed with VIMOS at the VLT using integral field spectroscopy. This sample covers well the less studied LIRG luminosity range and includes isolated disks, interacting systems, and mergers. The majority of the galaxies have two main kinematically distinct components. One component (i.e., narrow or systemic) extends over the whole line-emitting region and is characterized by small to intermediate velocity dispersions (i.e., sigma from 30 to 160 km s^-1). It traces the overall velocity field. The second component (broad) has in general a larger velocity dispersion (up to 320 km s^-1), mainly found in the inner regions and generally blueshifted with respect to the systemic component. Most of the objects (76%) are dominated by rotation, more relevant in LIRGs than in ULIRGs. Isolated disks, interacting galaxies, and merging systems define a sequence of increasing mean velocity dispersion, and decreasing velocity field amplitude.The LIRGs classified as isolated disks have similar velocity amplitudes but larger mean velocity dispersions (44 vs. 24 km s^-1) than local spirals, implying a larger turbulence and thicker disks. Interacting systems and mergers have values closer to those of low velocity dispersion ellipticals/lenticular galaxies (E/SOs). The (U)LIRGs classified as mergers have kinematic properties similar to those shown by the Lyman break analogs (LBAs). The dynamical masses range from \sim 0.04 m* to 1.4 m* (i.e., m* = 1.4x10^{11} Msun), with ULIRGs (M{dyn} sim 0.5 +/- 0.2 m*) being more massive than LIRGs by, on average, a factor of about 2. The mass ratio of individual pre-coalescence galaxies is <2.5 for most of the systems, confirming that most (U)LIRG mergers involve sub-m* galaxies of similar mass.

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arXiv2011

Characterization of optically-selected star forming knots in (U)LIRGs

(abridged)We present a comprehensive characterization of the general properties (luminosity functions, mass, size, ages, etc) of optically selected compact stellar objects (knots) in a representative sample of 32 low-z (U)LIRGs. We use ACS images from the Hubble Space Telescope in F435W and F814W bands. The galaxies in the sample represent different interaction phases and cover a wide luminosity range (11.46 \leq log (L_IR (Lsun)) \leq 12.54). With a median size of 32 pc, most of the nearly 3000 knots detected consists of complexes of star clusters. Some of the knots (~15%) are so blue that their colors indicate a young (i.e., < 30 Myr) and almost extinction-free population. There is a clear correlation of the mass of these blue knots with their radius, M \propto R^{1.91\pm0.14}, similar to that found in complexes of clusters in M51 and in Giant Molecular Clouds. This suggests that the star formation within the knots is proportional to the gas density at any given radius. The star formation of all the knots is characterized by luminosity functions (LFs) of the knots with slopes close to 2. Though, we see a marginally significant indication that the LF evolves with the interaction process, becoming steeper from early to advanced merger phases. Due to size-of-sample effects we are probably sampling knots in ULIRGs intrinsically more luminous (x4) than in less luminous systems. They also have sizes and are likely to have masses characteristic of clumps in galaxies at z \gtrsim 1. Knots in post-mergers are on average larger (x 1.3-2), more luminous (2 mag) in the I-band, and 0.5 mag redder than those in systems in earlier phases. Two scenarios are briefly discussed: (1) the likely presence of relatively high extinction in the most advanced mergers; (2) the dissolution of the less massive clusters and/or their coalescence into more massive, evolved superclusters.

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arXiv2010

VLT-VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies III: the atlas of the stellar and ionized gas distribution

LIRGs and ULIRGs are much more numerous at higher redshifts than locally, dominating the star-formation rate density at redshifts ~1 - 2. Therefore, they are important objects in order to understand how galaxies form and evolve through cosmic time. We aim to characterize the morphologies of the stellar continuum and the ionized gas (H_alpha) emissions from local sources, and investigate how they relate with the dynamical status and IR-luminosity of the sources. We use optical (5250 -- 7450 Å) integral field spectroscopic (IFS) data for a sample of 38 sources, taken with the VIMOS instrument, on the VLT. We present an atlas of IFS images of continuum emission, H_alpha emission, and H_alpha equivalent widths for the sample. The H_alpha images frequently reveal extended structures that are not visible in the continuum, such as HII regions in spiral arms, tidal tails, rings, of up to few kpc from the nuclear regions. The morphologies of the continuum and H_alpha images are studied on the basis of the C_{2kpc} parameter, which measures the concentration of the emission within the central 2 kpc. The C_{2kpc} values found for the H_alpha images are higher than those of the continuum for the majority (85%) of the objects in our sample. On the other hand, most of the objects in our sample (~62%) have more than half of their H_alpha emission outside the central 2 kpc. No clear trends are found between the values of C_{2kpc} and the IR-luminosity of the sources. On the other hand, our results suggest that the star formation in advance mergers and early-stage interactions is more concentrated than in isolated objects. We compared the H_alpha and infrared emissions as tracers of the star-formation activity. We find that the star-formation rates derived using the H_alpha luminosities generally underpredict those derived using the IR luminosities, even after accounting for reddening effects.

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arXiv2010

PMAS Optical Integral Field Spectroscopy of Luminous Infrared Galaxies. II.-- Spatially resolved stellar populations and excitation conditions

The general properties of luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) in the local universe are well known since large samples of these objects have been the subject of numerous spectroscopic works. There are, however, relatively few studies of large samples of LIRGs and ULIRGs using integral field spectroscopy (IFS). We analyze optical (3800-7200A) IFS data taken with the Potsdam Multi-Aperture Spectrophotometer (PMAS) of the central few kiloparsecs of 11 LIRGs. To study the stellar populations we fit the optical stellar continuum and the hydrogen recombination lines of selected regions. We analyze the excitation conditions of the gas using the spatially resolved properties of the brightest optical emission lines. The optical continua of the selected regions are well fitted with a combination of evolved (~0.7-10Gyr) and ionizing (1-20Myr) stellar populations. The latter is more obscured than the evolved population, and has visual extinctions in good agreement with those obtained from the Balmer decrement. Except for NGC 7771, there is no clear evidence for an important contribution to the optical light from an intermediate-aged population (~100-500Myr). Even after correcting for the presence of stellar absorption, a large fraction of spaxels with low observed equivalent widths of Halpha in emission still show enhanced [NII]/Halpha and [SII]/Halpha ratios. These ratios are likely to be produced by a combination of photoionization in HII regions and diffuse emission. These regions of enhanced ratios are generally coincident with low surface brightness HII regions and diffuse emission detected in the Halpha and Pa-alpha images. Using the PMAS line ratios and the NICMOS Pa-alpha photometry of HII regions we find that the fraction of diffuse emission in LIRGs varies from galaxy to galaxy, and it is generally less than 60% as found in other starburst galaxies. (Abridged)

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arXiv2010

VLT-VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies II. Evidence for shock ionization caused by tidal forces in the extra-nuclear regions of interacting and merging LIRGs

LIRGs are an important class of objects in the low-z universe bridging the gap between normal spirals and the strongly interacting and starbursting ULIRGs. Studies of their 2D physical properties are still lacking. We aim to understand the nature and origin of the ionization mechanisms operating in the extranuclear regions of LIRGs as a function of the interaction phase and L_IR by using IFS data obtained with VIMOS. Our analysis is based on over 25300 spectra of 32 LIRGs covering all types of morphologies and the entire 10^11-10^12 L_sun range. We found strong evidence for shock ionization, with a clear trend with the dynamical status of the system. Specifically, we quantified the variation with interaction phase of several line ratios indicative of the excitation degree. While the [NII]/Ha ratio does not show any significant change, the [SII]/Ha and [OI]/Ha ratios are higher for more advanced interaction stages. We constrained the main mechanisms causing the ionization in the extra-nuclear regions using diagnostic diagrams. Isolated systems are mainly consistent with ionization caused by young stars. Large fractions of the extra-nuclear regions in interacting pairs and more advanced mergers are consistent with ionization caused by shocks. This is supported by the relation between the excitation degree and the velocity dispersion of the ionized gas, which we interpret as evidence for shock ionization in interacting galaxies and advanced mergers but not in isolated galaxies. This relation does not show any dependence with L_IR. All this indicates that tidal forces play a key role in the origin of the ionizing shocks in the extra-nuclear regions. We also showed what appears to be a common [OI]/Ha-sigma relation for the extranuclear ionized gas in interacting (U)LIRGs. This needs to be investigated further with a larger sample of ULIRGs.

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arXiv2009

PMAS integral field spectroscopy of luminous infrared galaxies. I.- The atlas

In this paper we present PMAS optical (3800-7200A) IFS of the northern hemisphere portion of a volume-limited sample of 11 LIRGs. The PMAS observations typically cover the central ~5kpc and are complemented with HST/NICMOS images. For most LIRGs in our sample, the peaks of the continuum and gas (e.g., Halpha, [NII]) emissions coincide, unlike what is observed in local, strongly interacting ULIRGs. The only exceptions are galaxies with circumnuclear rings of star formation where the most luminous Halpha emitting regions are found in the rings rather than in the nuclei, and the displacements are well understood in terms of differences in the stellar populations. A large fraction of the nuclei of these LIRGs are classified as LINER and intermediate LINER/HII, or composite objects. The excitation conditions of the integrated emission depend on the relative contributions of HII regions and the diffuse emission to the line emission over the PMAS FoV. Galaxies dominated by high surface-brightness HII regions show integrated HII-like excitation. A few galaxies show slightly larger integrated [NII]/Halpha and [SII]/Halpha line ratios than the nuclear ones, probably because of more contribution from the diffuse emission. The Halpha velocity fields over the central few kpc are generally consistent, at least to first order, with rotational motions. The velocity fields of most LIRGs are similar to those of disk galaxies, in contrast to the highly perturbed fields of most local, strongly interacting ULIRGs. The peak of the Halpha velocity dispersion coincides with the position of the nucleus and is likely to be tracing mass. All these results are similar to the properties of z~1 LIRGs, and they highlight the importance of detailed studies of flux-limited samples of local LIRGs. (Abridged)

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arXiv2007

VLT-VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies. I. The sample and first results

(Ultra)Luminous Infrared Galaxies [(U)LIRGs] are much more numerous at cosmological distances than locally, and are likely precursors of elliptical galaxies. Our goal is to carry out an integral field spectroscopic survey of a representative sample of low redshift (z < 0.26) (U)LIRGs, covering different morphologies from spirals to mergers over the entire infrared luminosity range. The present study is based on optical IFS obtained with the VIMOS instrument on the VLT. The first results of this survey are presented here with the study of two galaxies representative of the two major morphological types observed in (U)LIRGs, interacting pairs and morphologically- regular, weakly-interacting spirals, respectively. We have found that IRAS 06076-2139 consists of two low-intermediate mass (0.15 and 0.4 m*) galaxies with relative velocities of ~ 550 km/s and, therefore, it is unlikely that they will merge. The VIMOS IFS has also discovered the presence of a rapidly expanding and rotating ring of gas in the southern galaxy (Gs), likely due to a nearly central head-on passage of an intruder about 140 million years ago. IRASF 12115-4656 is a spiral for which we have found a mass of 1.2 m*. The neutral gas (traced by the NaI doublet) and ionized gas components are spatially and kinematically decoupled. The analysis presented here illustrates the full potential of IFS in two important aspects: (i) the study of the kinematics and ionization structure of complex interacting/merging systems, and (2i) the study of the kinematics of the different gas phases, neutral (cool) and ionized (warm), traced by the NaD and Halpha lines, respectively. (abbreviated)

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arXiv2006

Integral field spectroscopy of the Luminous Infrared Galaxy Arp299 (IC694+NGC3690)

The luminous infrared galaxy Arp299 (IC694+NGC3690) is studied using optical integral field spectroscopy obtained with the INTEGRAL system, together with archival Hubble Space Telescope WFPC2 and NICMOS images. The stellar and ionized gas morphology shows lambda-dependent variations due to the combined effects of the dust internal extinction, and the nature and spatial distribution of the different ionizing sources. The two-dimensional ionization maps have revealed an off-nuclear conical structure of about 4 kpc in length, characterized by high excitation conditions and a radial gradient in the gas electron density. The apex of this structure coincides with B1 region of NGC3690 which, in turn, presents Seyfert-like ionization, high extinction and a high velocity dispersion. These results strongly support the hypothesis that B1 is the true nucleus of NGC3690, where an AGN is located. In the circumnuclear regions HII-like ionization dominates, while LINER-like ionization is found elsewhere. The Halpha emitting sources with ages from 3.3 to 7.2x10^6 years, have masses of between 6 and 680x10^6 Msun and contribute (extinction corrected) about 45% to the bolometric luminosity. The ionized (Halpha) and neutral (NaD) gas velocity fields show similar structure on scales of several hundred to about 1 kpc, indicating that these gas components are kinematically coupled. The kinematic structure is complex and on scales of about 0.2 kpc does not appear to be dominated by the presence of ordered, rotational motions. The large velocity dispersion measured in NGC3690 indicates that this galaxy is the most massive of the system. The low velocity amplitude and dispersion of the interface suggest that the ionized gas is slowly rotating or in a close to quiescent phase.

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arXiv2006

NICMOS Status

We provide an overview of the most important calibration aspects of the NICMOS instrument on board of HST. We describe the performance of the instrument after the installation of the NICMOS Cooling System, and show that the behavior of the instrument has become very stable and predictable. We detail the improvements made to the NICMOS pipeline and outline plans for future developments. The derivation of the absolute photometric zero-point calibration is described in detail. Finally, we describe and quantify a newly discovered count-rate dependent non-linearity in the NICMOS cameras. This new non-linearity is distinctly different from the total count dependent non-linearity that is well known for near-infrared detectors. We show that the non-linearity has a power law behavior, with pixels with high system, or vice versa, pixels with low count rate detecting slightly less than expected. The effect has a wavelength dependence with observations at the shortest wavelengths being the most affected (~0.05-0.1 mag per dex flux change at ~1 micron, 0.03 mag per dex at 1.6 micron).

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arXiv2005

Exploring the Potential of Integral Field Spectroscopy Observing Extrasolar Planet Transits: Ground Based Observations of the Atmospheric Na in HD209458b

We explore the use of Integral Field Spectroscopy (IFS) to observe extrasolar planet transits. Although this technique should find its full potential in space observations (e.g. JWST, TPF), we have tested its basics with ground based time series observations of HD209458b obtained with WHT+INTEGRAL during a transit. For this analysis we used 5550 spectra, obtained in 150 exposures during a period of >7 hours. We found that IFS offers 3 fundamental advantages with respect to previously used methods. (i) It improves the effective S/N in photon limited observations by distributing the light coming from the star into the 2 dimensions of the detector. (ii) This type of IFS data allows to 'auto-calibrate' instrumental and background effects. (iii) Since the star image characteristics as well as its photometric properties are extracted from the same data-cube, it is possible to decorrelate photometric instabilities induced by PSF variations. These data have also allowed us to explore the accuracy limits of ground based 'relative' spectrophotometry. This was done using a photometric index that probes the NaD lines, for which we obtained a nominal 1-sigma error of ~1.0x10^-4. This result, based on observations of only 1 transit, indicates that this type of ground observation can constrain the characterization of the transmission spectrum of extrasolar planets. The present observations are compatible with no extra NaD depression during the transit. Though this result seems to be inconsistent with the recently reported HST-STIS findings we point out its limited statistical meaning: the results disagree within 1-sigma, but agree within 2-sigma. We also give some recommenda-tions to instrument developers in order to enhance the efficiency of the method.

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