arXiv subjects

Francisco Nogueras-Lara

Publications and source records attributed to Francisco Nogueras-Lara.

46 records · Page 3Linked to original sources

arXiv2021

The nuclear star cluster and nuclear stellar disc of the Milky Way: Different stellar population and star formation history

The Milky Way's nuclear stellar disc (NSD) and nuclear star cluster (NSC) are the main features of the Galactic centre. Nevertheless, their observation is hampered by the extreme source crowding and high extinction. Hence, their relation and formation scenario are not fully clear yet. We aim at detecting the stellar populations from the NSC and the NSD along the line-of-sight towards the NSC, and assess whether they have different stellar populations and star formation histories. We analysed the colour-magnitude diagram, $K_s$ vs. $H-K_s$, of a region of $8.2'\times2.8'$ centred on the NSC, and detected two different stellar groups with different extinctions. We studied their red clumps to find the features associated to each of the stellar populations. We obtained that the two groups of stars correspond to the NSD and the NSC, and found that they have significantly different stellar populations and star formation histories. We detected a double red clump for the NSD population, in agreement with previous work, whereas the NSC presents a more complex structure well fitted by three Gaussian features. We created extinction maps to analyse the extinction variation between the detected stellar groups. We found that the high-extinction layer varies on smaller scales (arc-seconds), and that there is a difference of $A_{K_s}\sim0.6$\,mag between both extinction layers. Finally, we obtained that the distance towards each of the stellar populations is compatible with the Galactic centre distance, and found some evidence of a slightly closer distance for the NSD stars ($\sim360\pm200$\,pc).

astro-ph.GA↗

arXiv2021

Distance to three molecular clouds in the central molecular zone

The determination of absolute and relative distances of molecular clouds along the line-of-sight towards the central molecular zone (CMZ) is crucial to infer its orbital structure, dynamics, and to understand star formation in the clouds. Recent results by Zoccali et al. 2021 suggest that the G0.253 + 0.016 cloud (the Brick) does not belong to the CMZ. This motivated us to cross check their results computing the absolute and relative distance to the Brick and also to other two molecular clouds (the 50 km/s, and the 20 km/s clouds), and discuss their CMZ membership. We used the colour magnitude diagrams $K_s$ vs. $H-K_s$ to compare stars detected towards the target clouds with stars detected towards three reference regions in the nuclear stellar disc (NSD) and the Galactic bulge. We used red clump (RC) stars to estimate the distance to each region. We obtained that all the clouds present a double RC feature. Such a double RC has been reported in previous work for the NSD, but not for the bulge adjacent to it. We exclude the possibility that the different RC features are located at significantly different distances. The obtained absolute and relative distances are compatible with the Galactic centre distance ($\sim8$ kpc).

astro-ph.GA↗

arXiv2021

A KMOS survey of the nuclear disk of the Milky Way I: Survey design and metallicities

In the central few degrees of the bulge of the Milky Way there is a flattened structure of gas, dust and stars (the central molecular zone) similar to nuclear disks in other galaxies. Due to extreme foreground extinction we possess only sparse information about the (mostly old) stellar population of the nuclear disc. Here we present our KMOS spectroscopic survey of the stars in the nuclear disk reaching the old populations. In order to obtain an unbiased data set, we sample stars in the full extinction range along each line-of-sight. We also observe reference fields in neighboring regions of the Galactic bulge. Here we describe the design and execution of the survey and present first results. We obtain spectra and five spectral indices of 3113 stars with a median S/N of 67 and measure radial velocities for 3051 stars. Of those, 2735 sources have sufficient S/N to estimate temperatures and metallicities from indices. We derive metallicities using the CO 2-0 and Na I K-band spectral features, where we derive our own empirical calibration using metallicities obtained with higher resolution observations. We use 183 giant stars for calibration spanning in metallicity from -2.5 to 0.6 dex and covering temperatures of up to 5500 K. The derived index based metallicities deviate from the calibration values with a scatter of 0.32 dex. The internal uncertainty of our metallicities is likely smaller. We use these metallicity measurements together with the CO index to derive effective temperatures using literature relations. We publish the catalog here. Our data set complements Galactic surveys such as Gaia and APOGEE for the inner 200 pc radius of the Milky Way which is not readily accessible by those surveys due to extinction. We will use the derived properties in future papers for further analysis of the nuclear disk.

astro-ph.GA↗

arXiv2020

Jeans modelling of the Milky Way's nuclear stellar disc

The nuclear stellar disc (NSD) is a flattened stellar structure that dominates the gravitational potential of the Milky Way at Galactocentric radii $30 \lesssim R \lesssim 300{\, \rm pc}$. In this paper, we construct axisymmetric Jeans dynamical models of the NSD based on previous photometric studies and we fit them to line-of-sight kinematic data of APOGEE and SiO maser stars. We find that (i) the NSD mass is lower but consistent with the mass independently determined from photometry by Launhardt et al. (2002). Our fiducial model has a mass contained within spherical radius $r=100{\, \rm pc}$ of $M(r<100{\, \rm pc}) = 3.9 \pm 1 \times 10^8 {\, \rm M_\odot}$ and a total mass of $M_{\rm NSD} = 6.9 \pm 2 \times 10^8 {\, \rm M_\odot}$. (ii) The NSD might be the first example of a vertically biased disc, i.e. with ratio between the vertical and radial velocity dispersion $σ_z/σ_R>1$. Observations and theoretical models of the star-forming molecular gas in the central molecular zone suggest that large vertical oscillations may be already imprinted at stellar birth. However, the finding $σ_z/σ_R > 1$ depends on a drop in the velocity dispersion in the innermost few tens of parsecs, on our assumption that the NSD is axisymmetric, and that the available (extinction corrected) stellar samples broadly trace the underlying light and mass distributions, all of which need to be established by future observations and/or modelling. (iii) We provide the most accurate rotation curve to date for the innermost $500 {\, \rm pc}$ of our Galaxy.

astro-ph.GA↗

arXiv2020

GALACTICNUCLEUS: A high-angular-resolution JHKs imaging survey of the Galactic centre III. Evidence for wavelength dependence of the extinction curve in the near-infrared

The characterisation of the extinction curve in the near infrared (NIR) is fundamental to analyse the structure and stellar population of the Galactic centre (GC), whose analysis is hampered by the extreme interstellar extinction ($A_V\sim 30$ mag) that varies on arc-second scales. Recent studies indicate that the behaviour of the extinction curve might be more complex than previously assumed, pointing towards a variation of the extinction curve as a function of wavelength. We aim at analysing the variations of the extinction index, $α$, with wavelength, line-of-sight, and absolute extinction, extending previous analysis to a larger area of the innermost regions of the Galaxy. We analysed the whole GALACTICNUCLEUS survey, a high-angular resolution ($\sim 0.2''$) $JHK_s$ NIR survey specially designed to observe the GC in unprecedented detail. It covers a region of $\sim 6000$\,pc$^2$, comprising fields in the nuclear stellar disc, the inner bulge, and the transition region between them. We applied two independent methods based on red clump (RC) stars to constrain the extinction curve and analysed its variation superseding previous studies. We used more than 165,000 RC stars and increased significantly the size of the regions analysed to confirm that the extinction curve varies with the wavelength. We estimated a difference $Δα= 0.21\pm0.07$ between the obtained extinction indices, $α_{JH}=2.44\pm0.05$ and $α_{HK_s} = 2.23\pm0.05$. We also concluded that there is no significant variation of the extinction curve with wavelength, with the line-of-sight or the absolute extinction. Finally, we computed the ratios between extinctions, $A_J/A_H = 1.87\pm0.03$ and $A_{H}/A_{K_s} = 1.84\pm0.03$, consistent with all the regions of the GALACTICNUCLEUS catalogue.

astro-ph.GA↗

arXiv2019

Variability of the near-infrared extinction curve towards the Galactic centre

Due to the extreme extinction towards the Galactic centre ($A_{V} \sim 30$ mag), its stellar population is mainly studied in the near-infrared (NIR) regime. Therefore, a proper analysis of the NIR extinction curve is necessary to fully characterise the stellar structure and population of the inner part of the galaxy. We studied the dependence of the extinction index ($α_λ$) in the NIR on the line of sight, wavelength, and extinction. We used the GALACTICNUCLEUS imaging survey, a high angular resolution catalogue ($0.2''$) for the inner part of the Galaxy in $JHK_s$, and studied the spatial variation in the extinction index. We also applied two independent methods based on red clump stars to compute the extinction index between different bands and its variation with wavelength. We did not detect any significant line-of-sight or extinction variation in $α$ within the studied region in the nuclear stellar disc. The extinction index between $JH$ and $HK_s$ differs by $0.19 \pm 0.05$. We obtained mean values for the extinction indices $α_{JH} = 2.43\pm0.03$ and $α_{HK_s} = 2.23\pm0.03$. The dependence of the extinction index on the wavelength could explain the differences obtained for $α_λ$ in the literature since it was assumed constant for the NIR regime.

astro-ph.SR↗

arXiv2019

GALACTICNUCLEUS: A high-angular-resolution JHKs imaging survey of the Galactic centre II. First data release of the catalogue and the most detailed CMDs of the GC

The high extinction and extreme source crowding of the central regions of the Milky Way are serious obstacles to the study of the structure and stellar population of the Galactic centre (GC). Existing surveys that cover the GC region (2MASS, UKIDSS, VVV, SIRIUS) do not have the necessary high angular resolution. Therefore, a high-angular-resolution survey in the near infrared is crucial to improve the state of the art. Here, we present the GALACTICNUCLEUS catalogue, a near infrared $JHK_s$ high-angular-resolution ($0.2''$) survey of the nuclear bulge of the Milky Way. We explain in detail the data reduction, data analysis, calibration, and uncertainty estimation of the GALACTICNUCLEUS survey. We assess the data quality comparing our results with previous surveys. We obtained accurate $JHK_s$ photometry for $\sim 3.3\times10^6$ stars in the GC detecting around 20 \% in $J$, 65 \% in $H,$ and 90 \% in $K_s$. The survey covers a total area of $\sim0.3$ square degrees, which corresponds to $\sim 6,000$ pc$^2$. The GALACTICNUCLEUS survey reaches 5\,$σ$ detections for $J \sim 22$ mag, $H \sim 21$ mag, and $K_s \sim 21$ mag. The uncertainties are below 0.05 mag at $J \sim 21$ mag, $H \sim 19$ mag, and $K_s \sim 18$ mag. The zero point systematic uncertainty is $\lesssim0.04$ mag in all three bands. We present colour-magnitude diagrams for the different regions covered by the survey.

astro-ph.GA↗

arXiv2017

Near-Infrared Variability Study of the Central 2.3 arcmin x 2.3 arcmin of the Galactic Centre I. Catalog of Variable Sources

We used four-year baseline HST/WFC3 IR observations of the Galactic Centre in the F153M band (1.53 micron) to identify variable stars in the central ~2.3'x2.3' field. We classified 3845 long-term (periods from months to years) and 76 short-term (periods of a few days or less) variables among a total sample of 33070 stars. For 36 of the latter ones, we also derived their periods (<3 days). Our catalog not only confirms bright long period variables and massive eclipsing binaries identified in previous works, but also contains many newly recognized dim variable stars. For example, we found δScuti and RR Lyrae stars towards the Galactic Centre for the first time, as well as one BL Her star (period < 1.3 d). We cross-correlated our catalog with previous spectroscopic studies and found that 319 variables have well-defined stellar types, such as Wolf-Rayet, OB main sequence, supergiants and asymptotic giant branch stars. We used colours and magnitudes to infer the probable variable types for those stars without accurately measured periods or spectroscopic information. We conclude that the majority of unclassified variables could potentially be eclipsing/ellipsoidal binaries and Type II Cepheids. Our source catalog will be valuable for future studies aimed at constraining the distance, star formation history and massive binary fraction of the Milky Way nuclear star cluster.

astro-ph.GA↗

arXiv2017

Near-Infrared Variability Study of the Central 2.3 arcmin x 2.3 arcmin of the Galactic Centre II. Identification of RR Lyrae Stars in the Milky Way Nuclear Star Cluster

Because of strong and spatially highly variable interstellar extinction and extreme source crowding, the faint (K>15) stellar population in the Milky Way's nuclear cluster is still poorly studied. RR Lyrae stars provide us with a tool to estimate the mass of the oldest, relative dim stellar population. Recently, we analyzed HST/WFC3/IR observations of the central 2.3'x2.3' of the Milky Way and found 21 variable stars with periods between 0.2 and 1d. Here, we present a further comprehensive analysis of these stars. The period-luminosity relationship of RR Lyrae is used to derive their extinctions and distances. Using multiple approaches, we classify our sample as four RRc, four RRab and three candidates, ten binaries. Especially, the four RRabs show sawtooth light curves and fall exactly onto the Oosterhoff I division in the Bailey diagram. Compared to the RRabs reported by Minniti et al, 2016, our new RRabs have higher extinction (A_K>1.8) and should be closer to the Galactic Centre. The extinction and distance of one RRab match those for the nuclear star cluster given in previous works. We perform simulations and find that after correcting for incompleteness, there could be no more than 40 RRabs within the nuclear star cluster and in our field-of-view. Through comparing with the known globular clusters of the Milky Way, we estimate that if there exists an old, metal-poor (-1.5<[Fe/H]<-1) stellar population in the Milky Way nuclear star cluster on a scale of 5x5pc, then it contributes at most 4.7x10^5 solar mass, i.e., ~18% of the stellar mass.

astro-ph.GA↗

arXiv2017

IRTF/TEXES Observations of the HII Regions H1 and H2 in the Galactic Centre

We present new [Ne II] (12.8 micron) IRTF/TEXES observations of the Galactic Center HII regions H1 and H2, which are at a projected distance of ~11 pc from the center of the Galaxy. The new observations allow to map the radial velocity distributions of ionized gas. The high spectroscopic resolution (~4 km/s) helps us to disentangle different velocity components and enables us to resolve previous ambiguity regarding the nature of these sources. The spatial distributions of the intensity and radial velocity of the [Ne II] line are mapped. In H1, the intensity distributions of the Paschen-α(1.87 micron) and [Ne II] lines are significantly different, which suggests a strong variation of extinction across the HII region of A_K~0.56. The radial velocity distributions across these HII regions are consistent with the predictions of a bow-shock model for H1 and the pressure-driven model for H2. Furthermore, we find a concentration of bright stars in H2. These stars have similar H-K_s colors and can be explained as part of a 2 Myr old stellar cluster. H2 also falls on the orbit of the molecular clouds, suggested to be around Sgr A*. Our new results confirm what we had previously suggested: the O supergiant P114 in H1 is a runaway star, moving towards us through the -30-0 {km/s} molecular cloud, whereas the O If star P35 in H2 formed in-situ, and may mark the position of a so-far unknown small star cluster formed within the central 30 pc of the Galaxy.

astro-ph.GA↗