arXiv subjects

Francisco Nogueras-Lara

Publications and source records attributed to Francisco Nogueras-Lara.

At least 37 records · Page 2Linked to original sources

arXiv2026

Unveiling the 3D structure of the central molecular zone from stellar kinematics and photometry: The 50 and 20 km/s clouds

The central molecular zone (CMZ), surrounding the Galactic centre, is the largest reservoir of dense molecular gas in the Galaxy. Despite its relative proximity, the 3D structure of the CMZ remains poorly constrained, primarily due to projection effects. We aim to constrain the line-of-sight location of two molecular clouds in the CMZ -- the 50 and 20 km/s clouds -- and to investigate their possible physical connection using stellar kinematics and photometry. This study serves as a pilot for future applications across the full CMZ. We estimated the line-of-sight position of the clouds by analysing stellar kinematics, stellar densities, and stellar populations towards the cloud regions and a control field. We find an absence of westward moving stars in the cloud regions, which indicates that they lie on the near side of the CMZ. This interpretation is supported by the stellar density distributions. The similar behaviour observed in the two clouds, as well as in the region between them (the ridge), suggests that they are located at comparable distances and are physically linked. We also identified an intermediate-age stellar population (2-7 Gyr) in both regions, consistent with that observed on the near side of the CMZ. We estimated the line-of-sight distances at which the clouds and the ridge become kinematically detectable (i.e. where the proper motion component parallel to the Galactic plane differs from that of the control field at the 3 sigma level) by converting their measured proper motions parallel to the Galactic plane using a theoretical model of the stellar distribution. We find that the 50 and 20 km/s clouds are located at $43\pm8$ pc and $56\pm11$ pc from Sgr A*, respectively, and that the ridge lies at $56\pm11$ pc; this supports the idea that the clouds are physically connected through the ridge.

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arXiv2025

Rotation and stability of the circumnuclear gas disk in the Galactic Center potential by the ALMA CMZ Exploration Survey (ACES)

We investigated the gravitational potential and mass distribution in the Galactic Center by examining the morphology and kinematics of the circumnuclear gaseous disk revealed by the molecular line data from the ALMA CMZ Exploration Survey (ACES). We obtain an estimate of the shape of the potential {within the central $\sim 20$ pc} to reproduce the observed properties of the circumnuclear gas disk (CND) by simulating the motion of test particles for various axial ratios and show that the potential is approximately spherical. We construct a rotation curve by applying the terminal velocity method to the position-velocity diagrams, and calculate the mass distribution in the Galactic Center. The distribution of mass density is found to be of cusp type, approximated by $ρ_{\rm mass} \sim 1.56\times 10^5(R/1 {\rm pc})^{-1.9}~M_{\odot} {\rm pc}^{-3}$, where $R$ is the distance from the nucleus. We discuss the tidal effect caused by the gravitational potential that produces the rotation curve and show that the gas disk is stable against self-gravitational contraction within a critical radius of $ R_{\rm T}\sim 14 ~(ρ_{\rm gas}/10^5 {\rm H_2~cm^{-3}})^{-1/2}~{\rm pc}$. This suggests suppression of star formation and a top-heavy IMF in the circmunuclear region.

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arXiv2025

The JWST-NIRCam View of Sagittarius C. III. The Extinction Curve

Determining the infrared extinction curve towards the Galactic centre is crucial for accurately correcting observed data and deriving the underlying stellar populations. However, extinction curves reported in the literature often show discrepancies. We aim to derive the infrared extinction curve towards the Galactic centre based on JWST-NIRCam data for the first time, using observations of the Sagittarius C region in the 1-5 $μ$m range. We determined extinction ratios using two different methods, both based on measuring the reddening vector using the slope of red clump stars, whose intrinsic properties are well known, in observed colour-magnitude diagrams. The extinction curve derived in this work is in good agreement with previous results in the literature. We obtained the following extinction ratios relative to F162M: $A_\mathrm{F115W} : A_\mathrm{F162M} : A_\mathrm{F182M} : A_\mathrm{F212N} : A_\mathrm{F360M} : A_\mathrm{F405N} : A_\mathrm{F470N} : A_\mathrm{F480M} = 1.84 \pm 0.03 : 1.00 : 0.789 \pm 0.005 : 0.607 \pm 0.014 : 0.306 \pm 0.011 : 0.248 \pm 0.017 : 0.240 \pm 0.019 : 0.21 \pm 0.03$. Besides, we found different values of the extinction index for the short- ($λ\sim 1-2.5\,μ$m, $α\sim 2$) and long-wavelength ($λ\sim 2.5-5\,μ$m, $α\sim 1.4$) regimes, with the extinction curve flattening at longer wavelengths. Comparison with extinction curves derived both inside and outside the Galactic centre suggests that the infrared extinction curve does not significantly vary in the central regions, and shows no significant evidence for variations between different lines of sight beyond the inner Galaxy within the uncertainties.

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arXiv2025

Kinematic and extinction analysis of a potential spiral arm beyond the Galactic bar

Determining the structure of the Milky Way is essential for understanding its morphology, dynamics, and evolution. However, studying its innermost regions is challenging due to high extinction and crowding. The detection of a double red clump (RC; core-helium-burning stars) feature at very low Galactic latitudes suggests the presence of a spiral arm beyond the Galactic bar, providing new insights into the Galaxy's structure along this complex line of sight. We evaluate this possibility by analysing the proper motion and extinction distributions of the detected RC features. We constructed proper motion and extinction difference maps to investigate the kinematic and reddening properties of the RC populations, and the kinematic differences were validated using N-body simulations of a Milky Way-like galaxy. We find that the two RC features are kinematically distinct, with a relative proper motion difference of $-0.16\pm0.02\, mas/yr$ in the component parallel to the Galactic plane. This difference can be explained by Galactic rotation if the two RCs lie at different distances, consistent with the simulations. The extinction towards the secondary RC is also $\sim0.05$ mag higher than that of the primary RC. Additionally, we estimate that the extinction difference between the RC features corresponds to only $\sim5\%$ of the total extinction from Earth to the first RC, suggesting little interstellar material between the farthest edge of the Galactic bar and the kinematically distinct structure traced by the secondary RC. Using $JK_s$ photometry, we derive $A_J/A_{K_s}=3.34\pm0.07$, consistent with previous results and showing no significant variation across fields or along the line of sight. The results support the secondary clump tracing a distant structure, possibly a spiral arm, although we cannot exclude that the population belongs to the disc.

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arXiv2025

Circum-nuclear eccentric gas flow in the Galactic Center revealed by ALMA CMZ Exploration Survey (ACES)

We analyze the CS (J=2-1) line cube from the internal data release obtained by the large-scale program "ALMA CMZ Exploration Survey (ACES)" to investigate the kinematic structure of the innermost $\sim 10$ pc region of the Galaxy, which contains the high-velocity compact cloud (HVCC) at $(l,b,v_{\rm lsr})\sim(+0^\circ.02,-0^\circ.02, 100 {\rm km~s}^{-1})$ (hereafter G0.02). The longitude-velocity diagram (LVD) of the cloud draws an elliptical structure, which is interpreted as an orbital trajectory in the $(l,V_{\rm lsr})$ space of a noncircular (eccentric) motion of the molecular gas in the gravitational potential of an extended mass distribution in the central 10 pc of the Galaxy. We argue that G0.02 is a kinematic tracer of the inner potential, a rare case of a dense gas following an eccentric orbit in the nuclear gravitational field.

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arXiv2025

The SKA Galactic Centre Survey -- A White Paper

With its extreme density of stars and stellar remnants, dense young massive clusters, high specific star formation rate, intense radiation field, high magnetic field strength, and properties of the interstellar medium that resemble those in high redshift galaxies and starbursts, the Galactic Centre is the most extreme environment that we can observe in detail. It is also the only nucleus of a galaxy that we can observe with a resolution of just a few milli parsecs. This makes it a crucial target to understand the physics of galactic nuclei and star formation, as well as the connection between them. It enables studies of a large number of otherwise rare objects, such as extremely massive stars and stellar remnants, at a well-defined distance, thus facilitating the interpretation of their properties. The Galactic Centre has been and is being studied intensively with the most advanced facilities. In this White Paper, we advocate for a large-area, multi-wavelength survey with the Square Kilometre Array of an area of about 1.25x0.3 deg**2 (180x40 pc**2), centered on the massive black hole Sagittarius A* and for repeated deep observations of the nuclear star cluster over a decade, which will allow the community to address multiple science problems with a single data set.

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arXiv2024

The JWST-NIRCam View of Sagittarius C. II. Evidence for Magnetically Dominated HII Regions in the CMZ

We present JWST-NIRCam narrow-band, 4.05 $μ$m Brackett-$α$ images of the Sgr C HII region, located in the Central Molecular Zone (CMZ) of the Galaxy. Unlike any HII region in the Solar vicinity, the Sgr C plasma is dominated by filamentary structure in both Brackett-$α$ and the radio continuum. Some bright filaments, which form a fractured arc with a radius of about 1.85 pc centered on the Sgr C star-forming molecular clump, likely trace ionization fronts. The brightest filaments form a `$π$-shaped' structure in the center of the HII region. Fainter filaments radiate away from the surface of the Sgr C molecular cloud. The filaments are emitting optically thin free-free emission, as revealed by spectral index measurements from 1.28 GHz (MeerKAT) to 97 GHz (ALMA). But, the negative in-band 1 to 2 GHz spectral index in the MeerKAT data alone reveals the presence of a non-thermal component across the entire Sgr C HII region. We argue that the plasma flow in Sgr C is controlled by magnetic fields, which confine the plasma to rope-like filaments or sheets. This results in the measured non-thermal component of low-frequency radio emission plasma, as well as a plasma $β$ (thermal pressure divided by magnetic pressure) below 1, even in the densest regions. We speculate that all mature HII regions in the CMZ, and galactic nuclei in general, evolve in a magnetically dominated, low plasma $β$ regime.

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arXiv2024

The JWST-NIRCam View of Sagittarius C. I. Massive Star Formation and Protostellar Outflows

We present James Webb Space Telescope (JWST)-NIRCam observations of the massive star-forming molecular cloud Sagittarius C (Sgr C) in the Central Molecular Zone (CMZ). In conjunction with ancillary mid-IR and far-IR data, we characterize the two most massive protostars in Sgr C via spectral energy distribution (SED) fitting, estimating that they each have current masses of $m_* \sim 20\:M_\odot$ and surrounding envelope masses of $\sim 100\:M_\odot$. We report a census of lower-mass protostars in Sgr C via a search for infrared counterparts to mm continuum dust cores found with ALMA. We identify 88 molecular hydrogen outflow knot candidates originating from outflows from protostars in Sgr C, the first such unambiguous detections in the infrared in the CMZ. About a quarter of these are associated with flows from the two massive protostars in Sgr C; these extend for over 1 pc and are associated with outflows detected in ALMA SiO line data. An additional $\sim 40$ features likely trace shocks in outflows powered by lower-mass protostars throughout the cloud. We report the discovery of a new star-forming region hosting two prominent bow shocks and several other line-emitting features driven by at least two protostars. We infer that one of these is forming a high-mass star given an SED-derived mass of $m_* \sim 9\:M_\odot$ and associated massive ($\sim 90\:M_\odot$) mm core and water maser. Finally, we identify a population of miscellaneous Molecular Hydrogen Objects (MHOs) that do not appear to be associated with protostellar outflows.

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arXiv2024

A broad linewidth, compact, millimeter-bright molecular emission line source near the Galactic Center

A compact source, G0.02467-0.0727, was detected in ALMA \threemm observations in continuum and very broad line emission. The continuum emission has a spectral index $α\approx3.3$, suggesting that the emission is from dust. The line emission is detected in several transitions of CS, SO, and SO$_2$ and exhibits a line width FWHM $\approx160$ \kms. The line profile appears Gaussian. The emission is weakly spatially resolved, coming from an area on the sky $\lesssim1"$ in diameter ($\lesssim10^4$ AU at the distance of the Galactic Center; GC). The centroid velocity is $v_{LSR}\approx40$-$50$ \kms, which is consistent with a location in the Galactic Center. With multiple SO lines detected, and assuming local thermodynamic equilibrium (LTE) conditions, $T_\mathrm{LTE} = 13$ K, which is colder than seen in typical GC clouds, though we cannot rule out low-density, subthermally excited, warmer gas. Despite the high velocity dispersion, no emission is observed from SiO, suggesting that there are no strong ($\gtrsim10~\mathrm{km~s}^{-1}$) shocks in the molecular gas. There are no detections at other wavelengths, including X-ray, infrared, and radio. We consider several explanations for the Millimeter Ultra-Broad Line Object (MUBLO), including protostellar outflow, explosive outflow, collapsing cloud, evolved star, stellar merger, high-velocity compact cloud, intermediate mass black hole, and background galaxy. Most of these conceptual models are either inconsistent with the data or do not fully explain it. The MUBLO is, at present, an observationally unique object.

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arXiv2024

Hunting young stars in the Galactic centre. Hundreds of thousands of solar masses of young stars in the Sagittarius C region

The Galactic centre stands out as the most prolific star-forming environment of the Galaxy when averaged over volume. In the last 30 million years, it has witnessed the formation of $\sim10^6 M_\odot$ of stars. However, crowding and high extinction hamper their detection and, up to now, only a small fraction of the expected mass of young stars has been identified. We aim to detect hidden young stars at the Galactic centre by analysing the stellar population in Sagittarius (Sgr) C. This is a region at the western edge of the nuclear stellar disc whose HII emission makes it a perfect candidate to host young stars. We built dereddened luminosity functions for Sgr C and a control field in the central region of the nuclear stellar disc, and fitted them with a linear combination of theoretical models to analyse their stellar population. We find that Sgr C hosts several $10^5 M_\odot$ of young stars. We compared our results with the recently discovered young stellar population in Sgr B1, which is situated at the opposite edge of the nuclear stellar disc. We estimated that the Sgr C young stars are $\sim20$ Myr old, and likely show the next evolutionary step of the slightly younger stars in Sgr B1. Our findings contribute to addressing the discrepancy between the expected and the detected number of young stars in the Galactic centre, and shed light on their evolution in this extreme environment. As a secondary result, we find an intermediate-age stellar population in Sgr C ($\sim50$ % of its stellar mass with an age of between 2 and 7 Gyr), which is not present in the innermost regions of the nuclear stellar disc (dominated by stars >7 Gyr). This supports the existence of an age gradient and favours an inside-out formation of the nuclear stellar disc.

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arXiv2023

Kinematics of Galactic Centre clouds shaped by shear-seeded solenoidal turbulence

The Central Molecular Zone (CMZ; the central ~ 500 pc of the Galaxy) is a kinematically unusual environment relative to the Galactic disc, with high velocity dispersions and a steep size-linewidth relation of the molecular clouds. In addition, the CMZ region has a significantly lower star formation rate (SFR) than expected by its large amount of dense gas. An important factor in explaining the low SFR is the turbulent state of the star-forming gas, which seems to be dominated by rotational modes. However, the turbulence driving mechanism remains unclear. In this work, we investigate how the Galactic gravitational potential affects the turbulence in CMZ clouds. We focus on the CMZ cloud G0.253+0.016 (`the Brick'), which is very quiescent and unlikely to be kinematically dominated by stellar feedback. We demonstrate that several kinematic properties of the Brick arise naturally in a cloud-scale hydrodynamics simulation that takes into account the Galactic gravitational potential. These properties include the line-of-sight velocity distribution, the steepened size-linewidth relation, and the predominantly solenoidal nature of the turbulence. Within the simulation, these properties result from the Galactic shear in combination with the cloud's gravitational collapse. This is a strong indication that the Galactic gravitational potential plays a crucial role in shaping the CMZ gas kinematics, and is a major contributor to suppressing the SFR by inducing predominantly solenoidal turbulent modes.

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arXiv2023

Roman Early-Definition Astrophysics Survey Opportunity: Galactic Roman Infrared Plane Survey (GRIPS)

A wide-field near-infrared survey of the Galactic disk and bulge/bar(s) is supported by a large representation of the community of Galactic astronomers. The combination of sensitivity, angular resolution and large field of view make Roman uniquely able to study the crowded and highly extincted lines of sight in the Galactic plane. A ~1000 deg2 survey of the bulge and inner Galactic disk would yield an impressive dataset of ~120 billion sources and map the structure of our Galaxy. The effort would foster subsequent expansions in numerous dimensions (spatial, depth, wavelengths, epochs). Importantly, the survey would benefit from early defintion by the community, namely because the Galactic disk is a complex environment, and different science goals will require trade offs.

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arXiv2023

PHANGS-JWST First Results: A combined HST and JWST analysis of the nuclear star cluster in NGC 628

We combine archival HST and new JWST imaging data, covering the ultraviolet to mid-infrared regime, to morphologically analyze the nuclear star cluster (NSC) of NGC 628, a grand-design spiral galaxy. The cluster is located in a 200 pc x 400 pc cavity, lacking both dust and gas. We find roughly constant values for the effective radius (r_eff ~ 5 pc) and ellipticity (ε ~ 0.05), while the Sérsic index (n) and position angle (PA) drop from n ~ 3 to ~ 2 and PA ~ 130° to 90°, respectively. In the mid-infrared, r_eff ~ 12pc, ε ~ 0.4, and n ~ 1-1.5, with the same PA ~ 90°. The NSC has a stellar mass of log10 (M_nsc / M_Sun) = 7.06 +- 0.31, as derived through B-V, confirmed when using multi-wavelength data, and in agreement with the literature value. Fitting the spectral energy distribution, excluding the mid-infrared data, yields a main stellar population's age of (8 +- 3) Gyr with a metallicity of Z = 0.012 +- 0.006. There is no indication of any significant star formation over the last few Gyr. Whether gas and dust were dynamically kept out or evacuated from the central cavity remains unclear. The best-fit suggests an excess of flux in the mid-infrared bands, with further indications that the center of the mid-infrared structure is displaced with respect to the optical center of the NSC. We discuss five potential scenarios, none of them fully explaining both the observed photometry and structure.

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arXiv2022

A first glimpse at the line-of-sight structure of the Milky Way's nuclear stellar disc

The nuclear stellar disc (NSD) is a dense stellar structure at the centre of our Galaxy. Given its proximity, it constitutes a unique laboratory to understand other galactic nuclei. Nevertheless, the high crowding and extinction hamper its study, and even its morphology and kinematics are not yet totally clear. In this work we use NSD red clump stars, whose intrinsic properties are well known, to trace the kinematics of the NSD and to compute the distance and extinction towards the edges of the NSD. We used publicly available proper motion and photometric catalogues of the NSD to distinguish red clump stars by using a colour-magnitude diagram. We then applied a Gaussian mixture model to obtain the proper motion distribution, and computed the extinction and distance towards stars with different kinematics. We obtained that the proper motion distributions contain NSD stars rotating eastwards and westwards, plus some contamination from Galactic bulge/bar stars, in agreement with previous work. We computed the distance and extinction towards the eastward- and westward-moving stars and concluded that the latter are $\sim300$ pc beyond, indicating a similar structure along and across the line of sight, and consistent with an axisymmetric structure of the NSD. Moreover, we found that the extinction within the NSD is relatively low and accounts for less than 10 % of the total extinction of the stars belonging to the farthest edge of the NSD.

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arXiv2022

Kinematic data rebuild the Nuclear star cluster as the most metal rich region of the Galaxy

The Galactic centre (GC) is located at only 8 kpc from Earth and constitutes a unique template to understand Galactic nuclei. Nevertheless, the high crowding and extinction towards the GC hamper the study of its main stellar components, the nuclear stellar disc (NSD) and the nuclear star cluster (NSC). Recent work has suggested that the NSD and the NSC can be distinguished along the line of sight towards the NSC via the different extinction of their stars. This motivated us to analyse the proper motion, radial velocity, and the metallicity distributions of the different extinction groups. We use photometric, kinematic, and metallicity data to distinguish between probable NSD and NSC stars in a region centred on the NSC. We detected two different extinction groups of stars and obtained significantly different proper motion distributions for each of them, in agreement with the expected kinematics for the NSD and the NSC. We derived radial velocity maps that appear to be different for the NSD and the NSC. We also found different metallicities for each of the components, with the largest one measured for the most extinguished group of stars. We obtained that the metallicity distribution of each extinction group is best fitted by a bimodal distribution, indicating the presence of two metallicity components for each of them (a broad one slightly below solar metallicity, and a more metal rich narrower one, that is largest for the high extinction group of stars). We conclude that both extinction groups are distinct GC components with different kinematics and metallicity, and correspond to the NSD and the NSC. Therefore, it is possible to distinguish them via their different extinction. The high mean metallicity, $[M/H]\sim0.3$\,dex, obtained for the NSC metal rich stars, supports that the NSC is arguabily the most metal rich region of the Galaxy.

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arXiv2022

Detection of an excess of young stars in the Galactic center Sagittarius B1 region

The Milky Way's center is the closest galaxy nucleus and the most extreme environment of the Galaxy. Although its volume is less than 1% of that of the Galactic disk, up to 10% of all new-born stars in the Galaxy in the past 100 Myr formed there. Therefore, it constitutes a perfect laboratory to understand star formation under extreme conditions, similar to those in starburst or high-redshift galaxies. However, the only two known Galactic center young clusters account for <10% of the expected young stellar mass. We analyze the star formation history of Sagittarius (Sgr) B1, a Galactic center region associated with strong HII emission, and find evidence for the presence of several $10^5$ solar masses of young stars, that formed $\sim$10 Myr ago. We also detect the presence of intermediate age stars (2-7 Gyr) in Sgr B1 that appear to be rare (or absent) in the inner regions of the nuclear stellar disk, and might indicate inside out formation. Our results constitute a large step toward a better understanding of star formation at the Galactic center, such as the fate of young clusters, and the possibly different initial mass function in this region.

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arXiv2021

Distance and extinction to the Milky Way spiral arms along the Galactic centre line of sight

The position of the Sun inside the Milky Way's disc hampers the study of the spiral arm structure. We aim to analyse the spiral arms along the line-of-sight towards the Galactic centre (GC) to determine their distance, extinction, and stellar population. We use the GALACTICNUCLEUS survey, a JHKs high angular resolution photometric catalogue (0.2") for the innermost regions of the Galaxy. We fitted simple synthetic colour-magnitude models to our data via $χ^2$ minimisation. We computed the distance and extinction to the detected spiral arms. We also analysed the extinction curve and the relative extinction between the detected features. Finally, we built extinction-corrected Ks luminosity functions (KLFs) to study the stellar populations present in the second and third spiral arm features. We determined the mean distances to the spiral arms: $d1=1.6\pm0.2$, $d2=2.6\pm0.2$, $d3=3.9\pm0.3$, and $d4=4.5\pm0.2$ kpc, and the mean extinctions: $A_{H1}=0.35\pm0.08$, $A_{H2}=0.77\pm0.08$, $A_{H3}=1.68\pm0.08$, and $A_{H4}=2.30\pm0.08$ mag. We analysed the extinction curve in the near infrared for the stars in the spiral arms and found mean values of $A_J/A_{H}=1.89\pm0.11$ and $A_H/A_{K_s}=1.86\pm0.11$, in agreement with the results obtained for the GC. This implies that the shape of the extinction curve does not depend on distance or absolute extinction. We also built extinction maps for each spiral arm and obtained that they are homogeneous and might correspond to independent extinction layers. Finally, analysing the KLFs from the second and the third spiral arms, we found that they have similar stellar populations. We obtained two main episodes of star formation: $>6$ Gyr ($\sim60-70\%$ of the stellar mass), and $1.5-4$ Gyr ($\sim20-30\%$ of the stellar mass), compatible with previous work. We also detected recent star formation at a lower level ($\sim10\%$) for the third spiral arm.

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arXiv2021

GALACTICNUCLEUS: A high-angular-resolution $JHK_s$ imaging survey of the Galactic centre. IV. Extinction maps and de-reddened photometry

The extreme extinction ($A_V\sim30$\,mag) and its variation on arc-second scales towards the Galactic centre hamper the study of its stars. Their analysis is restricted to the near infrared (NIR) regime, where the extinction curve can be approximated by a broken power law. Therefore, correcting for extinction is fundamental to analyse the structure and stellar population of the central regions of our Galaxy. We aim to, (1) discuss different strategies to de-redden the photometry and check the usefulness of extinction; (2) build extinction maps for the NIR bands $JHK_s$ and make them publicly available; (3) create a de-reddened catalogue of the GALACTICNUCLEUS (GNS) survey, identifying foreground stars; and (4) perform a preliminary analysis of the de-reddened $K_s$ luminosity functions (KLFs). We used photometry from the GNS survey to create extinction maps for the whole catalogue. We took red clump (RC) and red giant stars of similar brightnesses as a reference to build the maps and de-reddened the GNS photometry. We discussed the limitations of the process and analysed non-linear effects of the de-reddening. We obtained high resolution ($\sim3''$) extinction maps with low uncertainties ($\lesssim5$\,\%) and computed average extinctions for each of the regions covered by the GNS. We checked that our maps effectively correct the differential extinction reducing the spread of the RC features by a factor of $\sim2$. We assessed the validity of the broken power law approach computing two equivalent extinction maps $A_H$ using either $JH$ and $HK_s$ photometry for the same reference stars and obtained compatible average extinctions within the uncertainties. Finally, we analysed de-reddened KLFs for different lines of sight and found that the regions belonging to the NSD contain a homogeneous stellar population that is significantly different from that in the innermost bulge regions.

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