المؤلفون: Tress, R. G., Sormani, M. C., Girichidis, P., Glover, S. C. O., Klessen, R. S., Smith, R. J., Sobacchi, E., Armillotta, L., Barnes, A. T., Battersby, C., Bogue, K. R. J., Brucy, N., Colzi, L., Federrath, C., García, P., Ginsburg, A., Göller, J., Hatchfield, H P., Henkel, C., Hennebelle, P., Henshaw, J. D., Hirschmann, M., Hu, Y., Kauffmann, J., Kruijssen, J. M. D., Lazarian, A., Lipman, D., Longmore, S. N., Morris, M. R., Nogueras-Lara, F., Petkova, M. A., Pillai, T. G. S., Rivilla, V. M., Sánchez-Monge, Á., Soler, J. D., Whitworth, D., Zhang, Q.

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies

الوصف: The interstellar medium in the Milky Way's Central Molecular Zone (CMZ) is known to be strongly magnetised, but its large-scale morphology and impact on the gas dynamics are not well understood. We explore the impact and properties of magnetic fields in the CMZ using three-dimensional non-self gravitating magnetohydrodynamical simulations of gas flow in an external Milky Way barred potential. We find that: (1) The magnetic field is conveniently decomposed into a regular time-averaged component and an irregular turbulent component. The regular component aligns well with the velocity vectors of the gas everywhere, including within the bar lanes. (2) The field geometry transitions from parallel to the Galactic plane near $z=0$ to poloidal away from the plane. (3) The magneto-rotational instability (MRI) causes an in-plane inflow of matter from the CMZ gas ring towards the central few parsecs of $0.01-0.1$ M$_\odot$ yr$^{-1}$ that is absent in the unmagnetised simulations. However, the magnetic fields have no significant effect on the larger-scale bar-driven inflow that brings the gas from the Galactic disc into the CMZ. (4) A combination of bar inflow and MRI-driven turbulence can sustain a turbulent vertical velocity dispersion of $\sigma_z \simeq 5$ km s$^{-1}$ on scales of $20$ pc in the CMZ ring. The MRI alone sustains a velocity dispersion of $\sigma_z \simeq 3$ km s$^{-1}$. Both these numbers are lower than the observed velocity dispersion of gas in the CMZ, suggesting that other processes such as stellar feedback are necessary to explain the observations. (5) Dynamo action driven by differential rotation and the MRI amplifies the magnetic fields in the CMZ ring until they saturate at a value that scales with the average local density as $B \simeq 102 (n/10^3 cm^{-3})^{0.33}$ $\mu$G. Finally, we discuss the implications of our results within the observational context in the CMZ.
Comment: submitted to A&A, comments welcome

الوصول الحر: http://arxiv.org/abs/2403.13048Test

المؤلفون: Nieuwmunster, N., Schultheis, M., Sormani, M., Fragkoudi, F., Nogueras-Lara, F., Schödel, R., McMillan, P.

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies

الوصف: While orbital analysis studies were so far mainly focused on the Galactic halo, it is possible now to do these studies in the heavily obscured region close to the Galactic Centre. We aim to do a detailed orbital analysis of stars located in the nuclear stellar disc (NSD) of the Milky Way allowing us to trace the dynamical history of this structure. We integrated orbits of the observed stars in a non-axisymmetric potential. We used a Fourier transform to estimate the orbital frequencies. We compared two orbital classifications, one made by eye and the other with an algorithm, in order to identify the main orbital families. We also compared the Lyapunov and the frequency drift techniques to estimate the chaoticity of the orbits. We identified several orbital families as chaotic, $z$-tube, $x$-tube, banana, fish, saucer, pretzel, 5:4, and 5:6 orbits. As expected for stars located in a NSD, the large majority of orbits are identified as $z$-tubes (or as a sub-family of $z$-tubes). Since the latter are parented by $x_{2}$ orbits, this result supports the contribution of the bar (in which $x_{2}$ orbits are dominant in the inner region) in the formation of the NSD. Moreover, most of the chaotic orbits are found to be contaminants from the bar or bulge which would confirm the predicted contamination from the most recent NSD models. Based on a detailed orbital analysis, we were able to classify orbits into various families, most of which are parented by $x_{2}$-type orbits, which are dominant in the inner part of the bar.
Comment: 19 pages, 25 figures, accepted in A&A

الوصول الحر: http://arxiv.org/abs/2403.00761Test

المؤلفون: Nogueras-Lara, F., Feldmeier-Krause, A., Schödel, R., Sormani, M. C., de Lorenzo-Cáceres, A., Mastrobuono-Battisti, A., Schultheis, M., Neumayer, N., Rich, R. M., Nieuwmunster, N.

المصدر: A&A 680, A75 (2023)

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies

الوصف: The innermost regions of most galaxies are characterised by the presence of extremely dense nuclear star clusters. Nevertheless, these clusters are not the only stellar component present in galactic nuclei, where larger stellar structures known as nuclear stellar discs, have also been found. Understanding the relation between nuclear star clusters and nuclear stellar discs is challenging due to the large distance towards other galaxies which limits their analysis to integrated light. The Milky Way's centre, at only 8 kpc, hosts a nuclear star cluster and a nuclear stellar disc, constituting a unique template to understand their relation and formation scenario. We aim to study the kinematics and stellar metallicity of stars from the Milky Way's nuclear star cluster and disc to shed light on the relation between these two Galactic centre components. We used publicly available photometric, proper motions, and spectroscopic catalogues to analyse a region of $\sim2.8'\times4.9'$ centred on the Milky Way's nuclear star cluster. We built colour magnitude diagrams, and applied colour cuts to analyse the kinematic and metallicity distributions of Milky Way's nuclear star cluster and disc stars with different extinction along the line of sight. We detect kinematics and metallicity gradients for the analysed stars along the line of sight towards the Milky Way's nuclear star cluster, suggesting a smooth transition between the nuclear stellar disc and cluster. We also find a bi-modal metallicity distribution for all the analysed colour bins, which is compatible with previous work on the bulk population of the nuclear stellar disc and cluster. Our results suggest that these two Galactic centre components might be part of the same structure with the Milky Way's nuclear stellar disc being the grown edge of the nuclear star cluster.
Comment: Accepted for publication in A&A. 13 pages, 9 figures

الوصول الحر: http://arxiv.org/abs/2309.07219Test

المؤلفون: Veena, V. S., Riquelme, D., Kim, W. -J., Menten, K. M., Schilke, P., Sormani, M. C., Banda-Barragan, W. E., Wyrowski, F., Fuller, G. A., Cheema, A.

المصدر: A&A 674, L15 (2023)

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena

الوصف: We report the discovery of a velocity coherent, funnel shaped ^13CO emission feature in the Galactic centre (GC) using data from the SEDIGISM survey. The molecular cloud appears as a low velocity structure (V_LSR=[-3.5, +3.5] km/s) with an angular extent of 0.95{\deg} x 1{\deg}, extending toward positive Galactic latitudes. The structure is offset from Sgr A* toward negative Galactic longitudes and spatially and morphologically correlates well with the northern lobe of the 430 pc radio bubble, believed to be the radio counterpart of the multiwavelength GC chimney. Spectral line observations in the frequency range of 85-116 GHz have been carried out using the IRAM 30 metre telescope toward 12 positions along the funnel-shaped emission. We examine the ^12C/^13C isotopic ratios using various molecules and their isotopologues. The mean ^12C/^13C isotope ratio (30.6+-2.9) is consistent with the structure located within inner 3 kpc of the Galaxy and possibly in the GC. The velocity of the molecular funnel is consistent with previous radio recombination line measurements of the northern lobe of radio bubble. Our multiwavelength analysis suggests that the funnel shaped structure extending over 100 pc above the Galactic plane is the molecular counterpart of the northern GC chimney.
Comment: Accepted for publication in A&A Letters

الوصول الحر: http://arxiv.org/abs/2306.06980Test

المؤلفون: Stuber, S. K., Schinnerer, E., Williams, T. G., Querejeta, M., Meidt, S., Emsellem, E., Barnes, A., Klessen, R. S., Leroy, A. K., Neumann, J., Sormani, M. C., Bigiel, F., Chevance, M., Dale, D., Faesi, C., Glover, S. C. O., Grasha, K., Kruijssen, J. M. D., Liu, D., Pan, H., Pety, J., Pinna, F., Saito, T., Usero, A., Watkins, E. J.

المصدر: A&A 676, A113 (2023)

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies

الوصف: The morphology of a galaxy stems from secular and environmental processes during its evolutionary history. Thus galaxy morphologies have been a long used tool to gain insights on galaxy evolution. We visually classify morphologies on cloud-scales based on the molecular gas distribution of a large sample of 79 nearby main-sequence galaxies, using 1'' resolution CO(2-1) ALMA observations taken as part of the PHANGS survey. To do so, we devise a morphology classification scheme for different types of bars, spiral arms (grand-design, flocculent, multi-arm and smooth), rings (central and non-central rings) similar to the well-established optical ones, and further introduce bar lane classes. In general, our cold gas based morphologies agree well with the ones based on stellar light. Both our bars as well as grand-design spiral arms are preferentially found at the higher mass end of our sample. Our gas-based classification indicates a potential for misidentification of unbarred galaxies in the optical when massive star formation is present. Central or nuclear rings are present in a third of the sample with a strong preferences for barred galaxies (59%). As stellar bars are present in 45$\pm$5% of our sample galaxies, we explore the utility of molecular gas as tracer of bar lane properties. We find that more curved bar lanes have a shorter radial extent in molecular gas and reside in galaxies with lower molecular to stellar mass ratios than those with straighter geometries. Galaxies display a wide range of CO morphology, and this work provides a catalogue of morphological features in a representative sample of nearby galaxies.
Comment: 17 pages, 14 figures (+ Appendix 9 pages, 4 figures). Accepted for publication in A&A

الوصول الحر: http://arxiv.org/abs/2305.17172Test

المؤلفون: Nogueras-Lara, F., Schultheis, M., Najarro, F., Sormani, M. C., Gadotti, D. A., Rich, R. M.

المصدر: A&A 671, L10 (2023)

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies

الوصف: The nuclear stellar disc (NSD) is a flat dense stellar structure at the heart of the Milky Way. Recent work has shown that analogous structures are common in the nuclei of external spiral galaxies, where there is evidence of an age gradient that indicates that they form inside-out. However, the characterisation of the age of the NSD stellar population along the line of sight is still missing due to its extreme source crowding and the high interstellar extinction towards the Galactic centre. We aim to characterise the age of the stellar population at different average Galactocentric NSD radii to investigate for the first time the presence of an age gradient along the line of sight. We selected two groups of stars at different NSD radii via their different extinction and proper motion distribution. We analysed their stellar population by fitting their de-reddened $K_s$ luminosity functions with a linear combination of theoretical models. We find significant differences in the stellar population at different NSD radii, indicating the presence of an age gradient along the line of sight. Our sample from the closest edge of the NSD contains a significant fraction ($\sim40 \%$ of its total stellar mass) of intermediate-age stars (2-7 Gyr) that is not present in the sample from stars deeper inside the NSD, in which $\sim90 \%$ of the stellar mass is older than 7 Gyr. Our results suggest that the NSD age distribution is similar to the one found in external galaxies and they imply that bar-driven processes observed in external galaxies are similarly at play in the Milky Way.
Comment: Accepted for publication in A&A. 7 pages, 6 figures

الوصول الحر: http://arxiv.org/abs/2302.02890Test

المؤلفون: Anastasopoulou, K., Ponti, G., Sormani, M. C., Locatelli, N., Haberl, F., Morris, M. R., Churazov, E. M., Schödel, R., Maitra, C., Campana, S., Di Teodoro, E. M., Jin, C., Khabibullin, I., Mondal, S., Sasaki, M., Zhang, Y., Zheng, X.

المصدر: A&A 671, A55 (2023)

مصطلحات موضوعية: Astrophysics - High Energy Astrophysical Phenomena

الوصف: The diffuse Fe XXV (6.7 keV) line emission observed in the Galactic ridge is widely accepted to be produced by a superposition of a large number of unresolved X-ray point sources. In the very central degrees of our Galaxy, however, the existence of an extremely hot ($\sim$7 keV) diffuse plasma is still under debate. In this work we measure the Fe XXV line emission using all available XMM-Newton observations of the Galactic centre (GC) and inner disc ($-10^{\circ}$$<\ell<10^{\circ}$, $-2^{\circ}Comment: 21 pages, 11 figures, 7 tables, accepted for publication in A&A

الوصول الحر: http://arxiv.org/abs/2301.04164Test

المؤلفون: Maconi, E., Soler, J. D., Reissl, S., Girichidis, P., Klessen, R. S., Hennebelle, P., Molinari, S., Testi, L., Smith, R. J., Sormani, M. C., Teh, J. W., Traficante, A.

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies

الوصف: We present a study of synthetic observations of polarized dust emission at 353 GHz as seen by an observer within a cavity in the interstellar medium (ISM). The cavity is selected from a magnetohydrodynamic simulation of the local ISM with time-dependent chemistry, star formation, and stellar feedback in form of supernova explosions with physical properties comparable to the Local Bubble ones. We find that the local density enhancement together with the coherent magnetic field in the cavity walls makes the selected candidate a translucent polarization filter to the emission coming from beyond its domains. This underlines the importance of studying the Local Bubble in further detail. The magnetic field lines inferred from synthetic dust polarization data are qualitatively in agreement with the all-sky maps of polarized emission at 353 GHz from the Planck satellite in the latitudes interval 15deg <= |b| <= 65deg. As our numerical simulation allows us to track the Galactic midplane only out to distances of 250 pc, we exclude the region |b|<15deg from our analysis. At large Galactic latitudes, our model exhibits a high degree of small-scale structures. On the contrary, the observed polarization pattern around the Galactic poles is relatively coherent and regular, and we argue that the global toroidal magnetic field of the Milky Way is important for explaining the data at |b| > 65deg. We show that from our synthetic polarization maps, it is difficult to distinguish between an open and a closed Galactic cap using the inferred magnetic field morphology alone.

الوصول الحر: http://arxiv.org/abs/2212.06598Test

المؤلفون: Elia, D., Molinari, S., Schisano, E., Soler, J. D., Merello, M., Russeil, D., Veneziani, M., Zavagno, A., Noriega-Crespo, A., Olmi, L., Benedettini, M., Hennebelle, P., Klessen, R. S., Leurini, S., Paladini, R., Pezzuto, S., Traficante, A., Eden, D. J., Martin, P. G., Sormani, M., Coletta, A., Colman, T., Plume, R., Maruccia, Y., Mininni, C., Liu, S. J.

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies

الوصف: We present a new derivation of the Milky Way's current star formation rate (SFR) based on the data of the Hi-GAL Galactic plane survey. We estimate the distribution of the SFR across the Galactic plane from the star-forming clumps identified in the Hi-GAL survey and calculate the total SFR from the sum of their contributions. The estimate of the global SFR amounts to $2.0 \pm 0.7$~M$_{\odot}$~yr$^{-1}$, of which $1.7 \pm 0.6$~M$_{\odot}$~yr$^{-1}$ coming from clumps with reliable heliocentric distance assignment. This value is in general agreement with estimates found in the literature of last decades. The profile of SFR density averaged in Galactocentric rings is found to be qualitatively similar to others previously computed, with a peak corresponding to the Central Molecular Zone and another one around Galactocentric radius $R_\mathrm{gal} \sim 5$~kpc, followed by an exponential decrease as $\log(\Sigma_\mathrm{SFR}/[\mathrm{M}_\odot~\mathrm{yr}^{-1}~\mathrm{kpc}^{-2}])=a\,R_\mathrm{gal}/[\mathrm{kpc}]+b $, with $a=-0.28 \pm 0.01$. In this regard, the fraction of SFR produced within and outside the Solar circle is 84\% and 16\%, respectively; the fraction corresponding to the far outer Galaxy ($R_\mathrm{gal} > 13.5$~kpc) is only 1\%. We also find that, for $R_\mathrm{gal}>3$~kpc, our data follow a power law as a function of density, similarly to the Kennicutt-Schmidt relation. Finally, we compare the distribution of the SFR density across the face-on Galactic plane and those of median parameters, such as temperature, luminosity/mass ratio and bolometric temperature, describing the evolutionary stage of Hi-GAL clumps. We found no clear correlation between the SFR and the clump evolutionary stage.
Comment: To be published in ApJ

الوصول الحر: http://arxiv.org/abs/2211.05573Test

المؤلفون: Wallace, J., Battersby, C., Mills, E. A. C., Henshaw, J. D., Sormani, M. C., Ginsburg, A., Barnes, A. T., Hatchfield, H. P., Glover, S. C. O., Anderson, L. D.

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies

الوصف: We report on the discovery of linear filaments observed in CO(1-0) emission for a $\sim2'$ field of view toward the Sgr E star forming region centered at (l,b)=(358.720$^\circ$, 0.011$^\circ$). The Sgr E region is thought to be at the turbulent intersection of the ''far dust lane'' associated with the Galactic bar and the Central Molecular Zone (CMZ). This region is subject to strong accelerations which are generally thought to inhibit star formation, yet Sgr E contains a large number of HII regions. We present $^{12}$CO(1-0), $^{13}$CO(1-0), and C$^{18}$O(1-0) spectral line observations from ALMA and provide measurements of the physical and kinematic properties for two of the brightest filaments. These filaments have widths (FWHM) of $\sim0.1$ pc and are oriented nearly parallel to the Galactic plane, with angles from the Galactic plane of $\sim2^\circ$. The filaments are elongated, with lower limit aspect ratios of $\sim$5:1. For both filaments we detect two distinct velocity components that are separated by about 15 km s$^{-1}$. In the C$^{18}$O spectral line data with $\sim$0.09 pc spatial resolution, we find that these velocity components have relatively narrow ($\sim$1-2 km s$^{-1}$) FWHM linewidths when compared to other sources towards the Galactic center. The properties of these filaments suggest that the gas in the Sgr E complex is being ''stretched'' as it is rapidly accelerated by the gravitational field of the Galactic bar while falling towards the CMZ, a result that could provide insight into the extreme environment surrounding this region and the large-scale processes which fuel this environment.
Comment: 20 pages, 17 figures, accepted for publication in ApJ

الوصول الحر: http://arxiv.org/abs/2209.11781Test