Studying synthetic column density maps and absorption spectra from galactic wind models

Galactic winds are multi-phase outflows that probe how feedback regulates the mass and metallicity of galaxies. Their cold phase, mainly observable with absorption lines, is often detected hundreds to thousands of pc away from the galactic plane and with velocities of hundreds of km $\rm s^{-1}$. To understand observations, it is important to theoretically study how such lines are produced via numerical simulations of cloud systems exposed to winds and starburst UV backgrounds. In this thesis we study the thermodynamics, ion populations, and ion absorption lines of cold and warm radiative clouds evolving from magnetised wind-cloud systems and an unmagnetised shock-multicloud model. We account for radiative cooling with two different cooling floors and magnetic fields with two different orientations. In our wind-cloud simulations, cold clouds survive the interaction with the wind for longer, since they are less exposed to instabilities, than warmer clouds. Magnetic fields have a larger influence on warm clouds than in cold clouds. If transverse to the wind direction, the field creates a shield that confines the expansion of the cloud, delaying its evaporation. In our shock-multicloud simulation, cold gas at large distances is not accelerated by ram-pressure, but, instead, precipitates from mixed gas out of thermal equilibrium. To study ion populations and create synthetic spectra, we developed a flexible python interface to link our PLUTO simulations to TRIDENT via the YT-package infrastructure and CLOUDY. Our ion population analysis reveals that setting different cooling floors and magnetic fields affect the column densities of several ions. H\,{\sc i}, O\,{\sc vi}, Mg\,{\sc ii}, C\,{\sc iii}, and Si\,{\sc iv} are more sensitive to the cooling floors, and H\,{\sc i}, Mg\,{\sc ii}, C\, {\sc iii}, and Si\, {\sc iv} can also trace the initial magnetic field direction, making them good candidates for comparisons with observations

Effetto Doppler e applicazioni astrofisiche

L’Effetto Doppler è il fenomeno fisico che descrive la variazione della frequenza osservata di un’onda quando la sorgente emittente e l’osservatore sono in moto relativo fra di loro. Esso può essere trattato in maniera classica, se l'onda ha una velocità di propagazione inferiore a quella della luce, o in maniera relativistica. In ambito astrofisico l'Effetto Doppler viene applicato alla radiazione elettromagnetica, unico segnale che ci giunge dai corpi celesti. Esso viene studiato tramite lo spostamento delle righe spettrali verso il rosso (redshift) o il blu (blueshift). Un'importante conseguenza di questo fenomeno è l'allargamento delle righe a causa dell'agitazione termica delle particelle in una nube di gas o dei moti di rotazione dei corpi. Inoltre, grazie alla misura delle velocità radiali con il metodo Doppler si possono ricercare esopianeti, sistemi di stelle binarie/multiple e si possono stimare le masse degli oggetti in esame. Infine, si parlerà di come il fenomeno è stato utile per il calcolo del tasso di espansione dell’Universo e di come il reshift cosmologico venga impiegato nella misura del look back time

The physical origins of gas in the circumgalactic medium using observationally-motivated TNG50 mocks

Absorbers in the spectrum of background objects probe the circumgalactic medium (CGM) surrounding galaxies, but its physical properties remain unconstrained. We use the cosmological hydrodynamical simulation TNG50 to statistically trace the origins of HI Ly-$\alpha$ absorbers around galaxies at $z = 0.5$ with stellar masses ranging from 10$^8$ to 10$^{11}$ M$_\odot$. We emulate observational CGM studies by considering all gas within a line of sight velocity range of $\pm 500$ km s$^{-1}$ from the central, to quantitatively assess the impact of other galaxy haloes and overdense gas in the IGM that intersect sightlines. The impact of satellites to the total absorber fraction is most significant at impact parameters $0.5 R_{\rm vir} < b < R_{\rm vir}$ and satellites with masses below typical detection limits ($M_* < 10^8$ M$_\odot$) account for 10 (40) per cent of absorbers that intersect any satellite bound to $10^{10}$ and $10^{11}$ $(10^9)$ M$_\odot$ centrals. After confirming outflows are more dominant along the minor axis, we additionally show that at least 20 per cent of absorbers exhibit no significant radial movement, indicating that absorbers can also trace quasi-static gas. The metallicity of absorbers also depends on the azimuthal angle, but this signal is largely driven by enriched inflowing and quasi-static gas. Our work shows that determining the stellar mass of galaxies at $z_{\rm abs}$ is essential to constrain the physical origin of the gas traced in absorption, which in turn is key to characterising the kinematics and distribution of gas and metals in the CGM.Comment: 23 pages, 13 figures. Accepted for publication in MNRA

The BarYon CYCLE Project (ByCycle): Identifying and Localizing MgII Metal Absorbers with Machine Learning

The upcoming ByCycle project on the VISTA/4MOST multi-object spectrograph will offer new prospects of using a massive sample of $\sim 1$ million high spectral resolution ($R$ = 20,000) background quasars to map the circumgalactic metal content of foreground galaxies (observed at $R$ = 4000 - 7000), as traced by metal absorption. Such large surveys require specialized analysis methodologies. In the absence of early data, we instead produce synthetic 4MOST high-resolution fibre quasar spectra. To do so, we use the TNG50 cosmological magnetohydrodynamical simulation, combining photo-ionization post-processing and ray tracing, to capture MgII ($\lambda2796$, $\lambda2803$) absorbers. We then use this sample to train a Convolutional Neural Network (CNN) which searches for, and estimates the redshift of, MgII absorbers within these spectra. For a test sample of quasar spectra with uniformly distributed properties ($\lambda_{\rm{MgII,2796}}$, $\rm{EW}_{\rm{MgII,2796}}^{\rm{rest}} = 0.05 - 5.15$ \AA, $\rm{SNR} = 3 - 50$), the algorithm has a robust classification accuracy of 98.6 per cent and a mean wavelength accuracy of 6.9 \AA. For high signal-to-noise spectra ($\rm{SNR > 20}$), the algorithm robustly detects and localizes MgII absorbers down to equivalent widths of $\rm{EW}_{\rm{MgII,2796}}^{\rm{rest}} = 0.05$ \AA. For the lowest SNR spectra ($\rm{SNR=3}$), the CNN reliably recovers and localizes EW$_{\rm{MgII,2796}}^{\rm{rest}}$ $\geq$ 0.75 \AA\, absorbers. This is more than sufficient for subsequent Voigt profile fitting to characterize the detected MgII absorbers. We make the code publicly available through GitHub. Our work provides a proof-of-concept for future analyses of quasar spectra datasets numbering in the millions, soon to be delivered by the next generation of surveys.Comment: 13 pages, 9 figures, 1 table. Accepted for publication in MNRA

MUSE-ALMA Halos XI: Gas flows in the circumgalactic medium

The flow of gas into and out of galaxies leaves traces in the circumgalactic medium which can then be studied using absorption lines towards background quasars. We analyse 27 log(N_HI) > 18.0 HI absorbers at z = 0.2 to 1.4 from the MUSE-ALMA Halos survey with at least one galaxy counterpart within a line of sight velocity of +/-500 km s^{-1}. We perform 3D kinematic forward modelling of these associated galaxies to examine the flow of dense, neutral gas in the circumgalactic medium. From the VLT/MUSE, HST broadband imaging and VLT/UVES and Keck/HIRES high-resolution UV quasar spectroscopy observations, we compare the impact parameters, star-formation rates and stellar masses of the associated galaxies with the absorber properties. We find marginal evidence for a bimodal distribution in azimuthal angles for strong HI absorbers, similar to previous studies of the MgII and OVI absorption lines. There is no clear metallicity dependence on azimuthal angle and we suggest a larger sample of absorbers are required to fully test the relationship predicted by cosmological hydrodynamical simulations. A case-by-case study of the absorbers reveals that ten per cent of absorbers are consistent with gas accretion, up to 30 per cent trace outflows while the remainder trace gas in the galaxy disk, the intragroup medium and low-mass galaxies below the MUSE detection limit. Our results highlight that the baryon cycle directly affects the dense neutral gas required for star-formation and plays a critical role in galaxy evolution.Comment: 13 pages, 6 figures, 12 pages of appendix. Accepted for publication in MNRA

The physical origins of gas in the circumgalactic medium using observationally motivated TNG50 mocks

International audienceAbsorbers in the spectrum of background objects probe the circumgalactic medium (CGM) surrounding galaxies, but its physical properties remain unconstrained. We use the cosmological hydrodynamical simulation TNG50 to statistically trace the origins of ${\rm H\, {\small I}}$ Ly α absorbers around galaxies at z = 0.5 with stellar masses ranging from 108 to 1011 M⊙. We emulate observational CGM studies by considering all gas within a line of sight velocity range of ±500 kms-1 from the central, to quantitatively assess the impact of other galaxy haloes and overdense gas in the IGM that intersect sightlines. We find that 75 per cent of ${\rm H\, {\small I}}$ absorbers with column densities \log [N(\mbox{{\rm H\, {\small I}}})/\rm {cm}^{-2}] 16.0 trace the central galaxy within ±150 (80) kms-1 of M* = 1010(108) M⊙ central galaxies. The impact of satellites to the total absorber fraction is most significant at impact parameters 0.5Rvir vir, and satellites with masses below typical detection limits (M* 8 M⊙) account for 10 (40) per cent of absorbers that intersect any satellite bound to 1010 and 1011 (109) M⊙ centrals. After confirming outflows are more dominant along the minor axis, we additionally show that at least 20 per cent of absorbers exhibit no significant radial movement, indicating that absorbers can also trace quasi-static gas. Our work shows that determining the stellar mass of galaxies at zabs is essential to constrain the physical origin of the gas traced in absorption, which in turn is key to characterizing the kinematics and distribution of gas and metals in the CGM

The BarYon CYCLE Project (ByCycle): Identifying and Localizing MgII Metal Absorbers with Machine Learning

International audienceThe upcoming ByCycle project on the VISTA/4MOST multi-object spectrograph will offer new prospects of using a massive sample of $\sim 1$ million high spectral resolution ($R$ = 20,000) background quasars to map the circumgalactic metal content of foreground galaxies (observed at $R$ = 4000 - 7000), as traced by metal absorption. Such large surveys require specialized analysis methodologies. In the absence of early data, we instead produce synthetic 4MOST high-resolution fibre quasar spectra. To do so, we use the TNG50 cosmological magnetohydrodynamical simulation, combining photo-ionization post-processing and ray tracing, to capture MgII ($\lambda2796$, $\lambda2803$) absorbers. We then use this sample to train a Convolutional Neural Network (CNN) which searches for, and estimates the redshift of, MgII absorbers within these spectra. For a test sample of quasar spectra with uniformly distributed properties ($\lambda_{\rm{MgII,2796}}$, $\rm{EW}_{\rm{MgII,2796}}^{\rm{rest}} = 0.05 - 5.15$Å, $\rm{SNR} = 3 - 50$), the algorithm has a robust classification accuracy of 98.6 per cent and a mean wavelength accuracy of 6.9 Å. For high signal-to-noise spectra ($\rm{SNR > 20}$), the algorithm robustly detects and localizes MgII absorbers down to equivalent widths of $\rm{EW}_{\rm{MgII,2796}}^{\rm{rest}} = 0.05$Å. For the lowest SNR spectra ($\rm{SNR=3}$), the CNN reliably recovers and localizes EW$_{\rm{MgII,2796}}^{\rm{rest}}$$\geq$ 0.75 Å absorbers. This is more than sufficient for subsequent Voigt profile fitting to characterize the detected MgII absorbers. We make the code publicly available through GitHub. Our work provides a proof-of-concept for future analyses of quasar spectra datasets numbering in the millions, soon to be delivered by the next generation of surveys

The BarYon CYCLE Project (ByCycle): Identifying and Localizing MgII Metal Absorbers with Machine Learning

International audienceThe upcoming ByCycle project on the VISTA/4MOST multi-object spectrograph will offer new prospects of using a massive sample of $\sim 1$ million high spectral resolution ($R$ = 20,000) background quasars to map the circumgalactic metal content of foreground galaxies (observed at $R$ = 4000 - 7000), as traced by metal absorption. Such large surveys require specialized analysis methodologies. In the absence of early data, we instead produce synthetic 4MOST high-resolution fibre quasar spectra. To do so, we use the TNG50 cosmological magnetohydrodynamical simulation, combining photo-ionization post-processing and ray tracing, to capture MgII ($\lambda2796$, $\lambda2803$) absorbers. We then use this sample to train a Convolutional Neural Network (CNN) which searches for, and estimates the redshift of, MgII absorbers within these spectra. For a test sample of quasar spectra with uniformly distributed properties ($\lambda_{\rm{MgII,2796}}$, $\rm{EW}_{\rm{MgII,2796}}^{\rm{rest}} = 0.05 - 5.15$Å, $\rm{SNR} = 3 - 50$), the algorithm has a robust classification accuracy of 98.6 per cent and a mean wavelength accuracy of 6.9 Å. For high signal-to-noise spectra ($\rm{SNR > 20}$), the algorithm robustly detects and localizes MgII absorbers down to equivalent widths of $\rm{EW}_{\rm{MgII,2796}}^{\rm{rest}} = 0.05$Å. For the lowest SNR spectra ($\rm{SNR=3}$), the CNN reliably recovers and localizes EW$_{\rm{MgII,2796}}^{\rm{rest}}$$\geq$ 0.75 Å absorbers. This is more than sufficient for subsequent Voigt profile fitting to characterize the detected MgII absorbers. We make the code publicly available through GitHub. Our work provides a proof-of-concept for future analyses of quasar spectra datasets numbering in the millions, soon to be delivered by the next generation of surveys