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  • Open Access
    Authors: 
    K. Kiiveri; Daniel Gruen; Alexis Finoguenov; Thomas Erben; L. van Waerbeke; Eli S. Rykoff; Lance Miller; Steffen Hagstotz; R. A. Dupke; J. Patrick Henry; +12 more
    Publisher: Oxford University Press (OUP)
    Countries: Finland, France, Italy

    The COnstrain Dark Energy with X-ray clusters (CODEX) sample contains the largest flux limited sample of X-ray clusters at $0.35 < z < 0.65$. It was selected from ROSAT data in the 10,000 square degrees of overlap with BOSS, mapping a total number of 2770 high-z galaxy clusters. We present here the full results of the CFHT CODEX program on cluster mass measurement, including a reanalysis of CFHTLS Wide data, with 25 individual lensing-constrained cluster masses. We employ $lensfit$ shape measurement and perform a conservative colour-space selection and weighting of background galaxies. Using the combination of shape noise and an analytic covariance for intrinsic variations of cluster profiles at fixed mass due to large scale structure, miscentring, and variations in concentration and ellipticity, we determine the likelihood of the observed shear signal as a function of true mass for each cluster. We combine 25 individual cluster mass likelihoods in a Bayesian hierarchical scheme with the inclusion of optical and X-ray selection functions to derive constraints on the slope $��$, normalization $��$, and scatter $��_{\ln ��| ��}$ of our richness-mass scaling relation model in log-space: $\left = ����+ ��$, with $��= \ln (M_{200c}/M_{\mathrm{piv}})$, and $M_{\mathrm{piv}} = 10^{14.81} M_{\odot}$. We find a slope $��= 0.49^{+0.20}_{-0.15}$, normalization $ \exp(��) = 84.0^{+9.2}_{-14.8}$ and $��_{\ln ��| ��} = 0.17^{+0.13}_{-0.09}$ using CFHT richness estimates. In comparison to other weak lensing richness-mass relations, we find the normalization of the richness statistically agreeing with the normalization of other scaling relations from a broad redshift range ($0.0 37 pages, 12 figures

  • Open Access
    Authors: 
    Martin Beech; Alison Illingworth; Peter Brown;
    Publisher: Oxford University Press (OUP)

    A search for metre-sized and larger exo-atmosphere Perseid meteoroids via their surface reflected sunlight has been made with the 1.2-m Elginfield Telescope. A total survey time of 9.66 h was accumulated during the nights of 2002 August 10, 11 and 12. To a limiting apparent magnitude of +17, we made no distinct detection of any large exo-atmosphere Perseid meteoroids. Our telescopic survey results constrain the upper limit to the spatial number density of metre-sized and larger Perseid meteoroids to be less than ∼3 × 10 −3 per 10 9 km 3 .W e have also analysed a data set of possible in-atmosphere Perseid fireball events detected by spacebased optical and infrared sensors. Operating at a detection threshold of magnitude −17, the space-based sensors have detected eight possible Perseid fireballs in the 15-d window, centred on the time of shower maximum, over the cumulative time interval from 1978 August to 2000 August. The space-based sensor data yield a spatial number density of ∼7 × 10 −8 per 10 9 km 3

  • Open Access
    Authors: 
    Sarah Appleby; Romeel Davé; K. Kraljic; Daniel Anglés-Alcázar; Desika Narayanan;
    Publisher: Oxford University Press (OUP)
    Countries: United Kingdom, Denmark
    Project: UKRI | DiRAC-2.5 DC - Operations... (ST/R000832/1), UKRI | DiRAC-2.5 - the pathway t... (ST/P002293/1), NSF | Collaborative Research: T... (1908137), UKRI | DiRAC: Memory Intensive 2... (ST/R002371/1), UKRI | DiRAC: Memory Intensive 2... (ST/S002502/1), NSF | Gas and Dust in Galaxies ... (1909153), NSF | Modeling Galaxies in the ... (1715206)

    We study specific star formation rate (sSFR) and gas profiles of star forming and green valley galaxies in the Simba cosmological hydrodynamic simulation. Star-forming galaxy half-light radii ($R_{\rm half}$) at $z=0$ and their evolution ($\propto(1+z)^{-0.78}$) agree with observations. Passive galaxy $R_{\rm half}$ agree with observations at high redshift, but by $z=0$ are too large, owing to numerical heating. We compare Simba $z=0$ sSFR radial profiles for star forming and green valley galaxies to observations. Simba shows strong central depressions in star formation rate (SFR), sSFR, and gas fraction in green valley galaxies and massive star-forming systems, qualitatively as observed, owing to black hole X-ray feedback, which pushes central gas outwards. Turning off X-ray feedback leads to centrally peaked sSFR profiles as in other simulations. In conflict with observations, Simba yields green valley galaxies with strongly dropping sSFR profiles beyond $\gtrsim R_{\rm half}$, regardless of AGN feedback. The central depression owes to lowering molecular gas content; the drop in the outskirts owes to reduced star formation efficiency. Simba's satellites have higher central sSFR and lower outskirts sSFR than centrals, in qualitative agreement with observations. At $z=2$ Simba does not show central depressions in massive star-forming galaxies, suggesting Simba's X-ray feedback should be more active at high-$z$. High resolution tests indicate central sSFR suppression is not sensitive to numerical resolution. Reproducing the central sSFR depression in $z=0$ green valley galaxies represents a unique success of Simba. The remaining discrepancies highlight the importance of SFR and gas profiles in constraining quenching mechanisms. 21 pages, 11 figures, accepted by MNRAS

  • Open Access
    Authors: 
    I. Kafando; Francis LeBlanc; Carmelle Robert;
    Publisher: Oxford University Press (OUP)
  • Open Access
    Authors: 
    Kelsey Hoffman; Jeremy S. Heyl;
    Publisher: Oxford University Press (OUP)

    We have investigated the crustal properties of neutron stars without fallback accretion. We have calculated the chemical evolution of the neutron star crust in three different cases (a modified Urca process without the thermal influence of a crust, a thick crust, and a direct Urca process with a thin crust) in order to determine the detailed composition of the envelope and atmosphere as the nuclear reactions freeze out. Using a nuclear reaction network up to technetium, we calculate the distribution of nuclei at various depths of the neutron star. The nuclear reactions quench when the cooling timescale is shorter than the inverse of the reaction rate. Trace light elements among the calculated isotopes may have enough time to float to the surface before the layer crystallizes and form the atmosphere or envelope of the neutron star. The composition of the neutron-star envelope determines the total photon flux from the surface, and the composition of the atmosphere determines the emergent spectrum. Our calculations using each of the three cooling models indicate that without accretion of fallback the neutron star atmospheres are dependent on the assumed cooling process of the neutron star. Each of the cooling methods have different elements composing the atmosphere: for the modified Urca process the atmosphere is $^{28}$Si, the thick crust has an atmosphere of $^{50}$Cr, and the thin crust has an atmosphere of $^{40}$Ca. In all three cases the atmospheres are composed of elements which are lighter then iron.

  • Open Access
    Authors: 
    James M. M. Lane; Julio F. Navarro; Azadeh Fattahi; Kyle A. Oman; Jo Bovy;
    Publisher: Oxford University Press (OUP)
    Countries: United Kingdom, Netherlands
    Project: EC | DMIDAS (786910)

    The Ophiuchus stream is a short arc-like stellar feature of uncertain origin located $\sim 5$ kpc North of the Galactic centre. New proper motions from the second $Gaia$ data release reconcile the direction of motion of stream members with the stream arc, resolving a puzzling mismatch reported in earlier work. We use N-body simulations to show that the stream is likely only on its second pericentric passage, and thus was formed recently. The simulations suggest that the entire disrupted progenitor is visible in the observed stream today, and that little further tidal debris lies beyond the ends of the stream. The luminosity, length, width, and velocity dispersion of the stream suggest a globular cluster (GC) progenitor substantially fainter and of lower surface brightness than estimated in previous work, and unlike any other known globulars in the Galaxy. This result suggests the existence of clusters that would extend the known GC population to fainter and more weakly bound systems than hitherto known. How such a weakly-bound cluster of old stars survived until it was disrupted so recently, however, remains a mystery. Integrating backwards in time, we find that the orbits of Sagittarius and Ophiuchus passed within $\sim 5$ kpc of each other about $\sim 100$ Myrs ago, an interaction that might help resolve this puzzle. 11 pages, 7 figures, submitted to MNRAS

  • Open Access
    Authors: 
    Rok Roškar; Davide Fiacconi; Lucio Mayer; Stelios Kazantzidis; Thomas R. Quinn; James Wadsley;
    Publisher: Oxford University Press (OUP)
    Country: Switzerland
    Project: SNSF | Galaxy formation and mass... (152960)

    Monthly Notices of the Royal Astronomical Society, 449 (1) ISSN:0035-8711 ISSN:1365-2966 ISSN:1365-8711

  • Open Access
    Authors: 
    Aldo Mura-Guzmán; David Yong; C. Abate; Amanda I. Karakas; Chiaki Kobayashi; Heeyoung Oh; S. H. Chun; Gregory N. Mace;
    Publisher: Oxford University Press (OUP)
    Project: UKRI | Hertfordshire Astronomy 2... (ST/R000905/1), UKRI | BRIdging Disciplines of G... (ST/M000958/1)

    We present new fluorine abundance estimations in two carbon enhanced metal-poor (CEMP) stars, HE 1429-0551 and HE 1305+0007. HE 1429-0551 is also enriched in slow neutron-capture process (s-process) elements, a CEMP-s, and HE 1305+0007 is enhanced in both, slow and rapid neutron-capture process elements, a CEMP-s/r. The F abundances estimates are derived from the vibration-rotation transition of the HF molecule at 23358.6 A using high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrometer (IGRINS) at the 4m-class Lowell Discovery Telescope. Our results include a F abundance measurement in HE 1429-0551 of A(F) = +3.93 ([F/Fe] = +1.90) at [Fe/H] = -2.53, and a F upper limit in HE 1305+0007 of A(F) < +3.28 ([F/Fe] < +1.00) at [Fe/H] = -2.28. Our new derived F abundance in HE 1429-0551 makes this object the most metal-poor star where F has been detected. We carefully compare these results with literature values and state-of-the-art CEMP-s model predictions including detailed AGB nucleosynthesis and binary evolution. The modelled fluorine abundance for HE 1429-0551 is within reasonable agreement with our observed abundance, although is slightly higher than our observed value. For HE 1429-0551, our findings support the scenario via mass transfer by a primary companion during its thermally-pulsing phase. Our estimated upper limit in HE 1305+0007, along with data from the literature, shows large discrepancies compared with AGB models. The discrepancy is principally due to the simultaneous s- and r-process element enhancements which the model struggles to reproduce. 12 pages, 5 Figures -- Accepted in MNRAS

  • Open Access
    Authors: 
    Sijie Yu; James S. Bullock; Andrew Wetzel; Robyn E. Sanderson; Andrew S. Graus; Michael Boylan-Kolchin; Anna Nierenberg; Michael Y. Grudić; Philip F. Hopkins; Dušan Kereš; +1 more
    Publisher: Oxford University Press (OUP)
    Country: United States

    We study stellar-halo formation using six Milky Way-mass galaxies in FIRE-2 cosmological zoom simulations. We find that $5-40\%$ of the outer ($50-300$ kpc) stellar halo in each system consists of $\textit{in-situ}$ stars that were born in outflows from the main galaxy. Outflow stars originate from gas accelerated by super-bubble winds, which can be compressed, cool, and form co-moving stars. The majority of these stars remain bound to the halo and fall back with orbital properties similar to the rest of the stellar halo at $z=0$.In the outer halo, outflow stars are more spatially homogeneous, metal rich, and alpha-element-enhanced than the accreted stellar halo. At the solar location, up to $\sim 10 \%$ of our kinematically-identified halo stars were born in outflows; the fraction rises to as high as $\sim 40\%$ for the most metal-rich local halo stars ([Fe/H] $> -0.5$). We conclude that the Milky Way stellar halo could contain local counterparts to stars that are observed to form in molecular outflows in distant galaxies. Searches for such a population may provide a new, near-field approach to constraining feedback and outflow physics. A stellar halo contribution from outflows is a phase-reversal of the classic halo formation scenario of Eggen, Lynden-Bell $\&$ Sandange, who suggested that halo stars formed in rapidly $\textit{infalling}$ gas clouds. Stellar outflows may be observable in direct imaging of external galaxies and could provide a source for metal-rich, extreme velocity stars in the Milky Way. 19 pages, 20 figures, submitted to MNRAS

  • Open Access
    Authors: 
    Cora Uhlemann; Sandrine Codis; C. Pichon; Francis Bernardeau; Paulo H. F. Reimberg;
    Publisher: Oxford University Press (OUP)
    Country: France

    We present a first principle approach to obtain analytical predictions for spherically-averaged cosmic densities in the mildly non-linear regime that go well beyond what is usually achieved by standard perturbation theory. A large deviation principle allows us to compute the leading-order cumulants of average densities in concentric cells. In this symmetry, the spherical collapse model leads to cumulant generating functions that are robust for finite variances and free of critical points when logarithmic density transformations are implemented. They yield in turn accurate density probability distribution functions (PDFs) from a straightforward saddle-point approximation valid for all density values. Based on this easy-to-implement modification, explicit analytic formulas for the evaluation of the one- and two-cell PDF are provided. The theoretical predictions obtained for the PDFs are accurate to a few percent compared to the numerical integration, regardless of the density under consideration and in excellent agreement with N-body simulations for a wide range of densities. This formalism should prove valuable for accurately probing the quasi-linear scales of low redshift surveys for arbitrary primordial power spectra. 13 pages, 11 figures, minor corrections and added references, accepted for publication in MNRAS

Include:
5,169 Research products, page 1 of 517
  • Open Access
    Authors: 
    K. Kiiveri; Daniel Gruen; Alexis Finoguenov; Thomas Erben; L. van Waerbeke; Eli S. Rykoff; Lance Miller; Steffen Hagstotz; R. A. Dupke; J. Patrick Henry; +12 more
    Publisher: Oxford University Press (OUP)
    Countries: Finland, France, Italy

    The COnstrain Dark Energy with X-ray clusters (CODEX) sample contains the largest flux limited sample of X-ray clusters at $0.35 < z < 0.65$. It was selected from ROSAT data in the 10,000 square degrees of overlap with BOSS, mapping a total number of 2770 high-z galaxy clusters. We present here the full results of the CFHT CODEX program on cluster mass measurement, including a reanalysis of CFHTLS Wide data, with 25 individual lensing-constrained cluster masses. We employ $lensfit$ shape measurement and perform a conservative colour-space selection and weighting of background galaxies. Using the combination of shape noise and an analytic covariance for intrinsic variations of cluster profiles at fixed mass due to large scale structure, miscentring, and variations in concentration and ellipticity, we determine the likelihood of the observed shear signal as a function of true mass for each cluster. We combine 25 individual cluster mass likelihoods in a Bayesian hierarchical scheme with the inclusion of optical and X-ray selection functions to derive constraints on the slope $��$, normalization $��$, and scatter $��_{\ln ��| ��}$ of our richness-mass scaling relation model in log-space: $\left = ����+ ��$, with $��= \ln (M_{200c}/M_{\mathrm{piv}})$, and $M_{\mathrm{piv}} = 10^{14.81} M_{\odot}$. We find a slope $��= 0.49^{+0.20}_{-0.15}$, normalization $ \exp(��) = 84.0^{+9.2}_{-14.8}$ and $��_{\ln ��| ��} = 0.17^{+0.13}_{-0.09}$ using CFHT richness estimates. In comparison to other weak lensing richness-mass relations, we find the normalization of the richness statistically agreeing with the normalization of other scaling relations from a broad redshift range ($0.0 37 pages, 12 figures

  • Open Access
    Authors: 
    Martin Beech; Alison Illingworth; Peter Brown;
    Publisher: Oxford University Press (OUP)

    A search for metre-sized and larger exo-atmosphere Perseid meteoroids via their surface reflected sunlight has been made with the 1.2-m Elginfield Telescope. A total survey time of 9.66 h was accumulated during the nights of 2002 August 10, 11 and 12. To a limiting apparent magnitude of +17, we made no distinct detection of any large exo-atmosphere Perseid meteoroids. Our telescopic survey results constrain the upper limit to the spatial number density of metre-sized and larger Perseid meteoroids to be less than ∼3 × 10 −3 per 10 9 km 3 .W e have also analysed a data set of possible in-atmosphere Perseid fireball events detected by spacebased optical and infrared sensors. Operating at a detection threshold of magnitude −17, the space-based sensors have detected eight possible Perseid fireballs in the 15-d window, centred on the time of shower maximum, over the cumulative time interval from 1978 August to 2000 August. The space-based sensor data yield a spatial number density of ∼7 × 10 −8 per 10 9 km 3

  • Open Access
    Authors: 
    Sarah Appleby; Romeel Davé; K. Kraljic; Daniel Anglés-Alcázar; Desika Narayanan;
    Publisher: Oxford University Press (OUP)
    Countries: United Kingdom, Denmark
    Project: UKRI | DiRAC-2.5 DC - Operations... (ST/R000832/1), UKRI | DiRAC-2.5 - the pathway t... (ST/P002293/1), NSF | Collaborative Research: T... (1908137), UKRI | DiRAC: Memory Intensive 2... (ST/R002371/1), UKRI | DiRAC: Memory Intensive 2... (ST/S002502/1), NSF | Gas and Dust in Galaxies ... (1909153), NSF | Modeling Galaxies in the ... (1715206)

    We study specific star formation rate (sSFR) and gas profiles of star forming and green valley galaxies in the Simba cosmological hydrodynamic simulation. Star-forming galaxy half-light radii ($R_{\rm half}$) at $z=0$ and their evolution ($\propto(1+z)^{-0.78}$) agree with observations. Passive galaxy $R_{\rm half}$ agree with observations at high redshift, but by $z=0$ are too large, owing to numerical heating. We compare Simba $z=0$ sSFR radial profiles for star forming and green valley galaxies to observations. Simba shows strong central depressions in star formation rate (SFR), sSFR, and gas fraction in green valley galaxies and massive star-forming systems, qualitatively as observed, owing to black hole X-ray feedback, which pushes central gas outwards. Turning off X-ray feedback leads to centrally peaked sSFR profiles as in other simulations. In conflict with observations, Simba yields green valley galaxies with strongly dropping sSFR profiles beyond $\gtrsim R_{\rm half}$, regardless of AGN feedback. The central depression owes to lowering molecular gas content; the drop in the outskirts owes to reduced star formation efficiency. Simba's satellites have higher central sSFR and lower outskirts sSFR than centrals, in qualitative agreement with observations. At $z=2$ Simba does not show central depressions in massive star-forming galaxies, suggesting Simba's X-ray feedback should be more active at high-$z$. High resolution tests indicate central sSFR suppression is not sensitive to numerical resolution. Reproducing the central sSFR depression in $z=0$ green valley galaxies represents a unique success of Simba. The remaining discrepancies highlight the importance of SFR and gas profiles in constraining quenching mechanisms. 21 pages, 11 figures, accepted by MNRAS

  • Open Access
    Authors: 
    I. Kafando; Francis LeBlanc; Carmelle Robert;
    Publisher: Oxford University Press (OUP)
  • Open Access
    Authors: 
    Kelsey Hoffman; Jeremy S. Heyl;
    Publisher: Oxford University Press (OUP)

    We have investigated the crustal properties of neutron stars without fallback accretion. We have calculated the chemical evolution of the neutron star crust in three different cases (a modified Urca process without the thermal influence of a crust, a thick crust, and a direct Urca process with a thin crust) in order to determine the detailed composition of the envelope and atmosphere as the nuclear reactions freeze out. Using a nuclear reaction network up to technetium, we calculate the distribution of nuclei at various depths of the neutron star. The nuclear reactions quench when the cooling timescale is shorter than the inverse of the reaction rate. Trace light elements among the calculated isotopes may have enough time to float to the surface before the layer crystallizes and form the atmosphere or envelope of the neutron star. The composition of the neutron-star envelope determines the total photon flux from the surface, and the composition of the atmosphere determines the emergent spectrum. Our calculations using each of the three cooling models indicate that without accretion of fallback the neutron star atmospheres are dependent on the assumed cooling process of the neutron star. Each of the cooling methods have different elements composing the atmosphere: for the modified Urca process the atmosphere is $^{28}$Si, the thick crust has an atmosphere of $^{50}$Cr, and the thin crust has an atmosphere of $^{40}$Ca. In all three cases the atmospheres are composed of elements which are lighter then iron.

  • Open Access
    Authors: 
    James M. M. Lane; Julio F. Navarro; Azadeh Fattahi; Kyle A. Oman; Jo Bovy;
    Publisher: Oxford University Press (OUP)
    Countries: United Kingdom, Netherlands
    Project: EC | DMIDAS (786910)

    The Ophiuchus stream is a short arc-like stellar feature of uncertain origin located $\sim 5$ kpc North of the Galactic centre. New proper motions from the second $Gaia$ data release reconcile the direction of motion of stream members with the stream arc, resolving a puzzling mismatch reported in earlier work. We use N-body simulations to show that the stream is likely only on its second pericentric passage, and thus was formed recently. The simulations suggest that the entire disrupted progenitor is visible in the observed stream today, and that little further tidal debris lies beyond the ends of the stream. The luminosity, length, width, and velocity dispersion of the stream suggest a globular cluster (GC) progenitor substantially fainter and of lower surface brightness than estimated in previous work, and unlike any other known globulars in the Galaxy. This result suggests the existence of clusters that would extend the known GC population to fainter and more weakly bound systems than hitherto known. How such a weakly-bound cluster of old stars survived until it was disrupted so recently, however, remains a mystery. Integrating backwards in time, we find that the orbits of Sagittarius and Ophiuchus passed within $\sim 5$ kpc of each other about $\sim 100$ Myrs ago, an interaction that might help resolve this puzzle. 11 pages, 7 figures, submitted to MNRAS

  • Open Access
    Authors: 
    Rok Roškar; Davide Fiacconi; Lucio Mayer; Stelios Kazantzidis; Thomas R. Quinn; James Wadsley;
    Publisher: Oxford University Press (OUP)
    Country: Switzerland
    Project: SNSF | Galaxy formation and mass... (152960)

    Monthly Notices of the Royal Astronomical Society, 449 (1) ISSN:0035-8711 ISSN:1365-2966 ISSN:1365-8711

  • Open Access
    Authors: 
    Aldo Mura-Guzmán; David Yong; C. Abate; Amanda I. Karakas; Chiaki Kobayashi; Heeyoung Oh; S. H. Chun; Gregory N. Mace;
    Publisher: Oxford University Press (OUP)
    Project: UKRI | Hertfordshire Astronomy 2... (ST/R000905/1), UKRI | BRIdging Disciplines of G... (ST/M000958/1)

    We present new fluorine abundance estimations in two carbon enhanced metal-poor (CEMP) stars, HE 1429-0551 and HE 1305+0007. HE 1429-0551 is also enriched in slow neutron-capture process (s-process) elements, a CEMP-s, and HE 1305+0007 is enhanced in both, slow and rapid neutron-capture process elements, a CEMP-s/r. The F abundances estimates are derived from the vibration-rotation transition of the HF molecule at 23358.6 A using high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrometer (IGRINS) at the 4m-class Lowell Discovery Telescope. Our results include a F abundance measurement in HE 1429-0551 of A(F) = +3.93 ([F/Fe] = +1.90) at [Fe/H] = -2.53, and a F upper limit in HE 1305+0007 of A(F) < +3.28 ([F/Fe] < +1.00) at [Fe/H] = -2.28. Our new derived F abundance in HE 1429-0551 makes this object the most metal-poor star where F has been detected. We carefully compare these results with literature values and state-of-the-art CEMP-s model predictions including detailed AGB nucleosynthesis and binary evolution. The modelled fluorine abundance for HE 1429-0551 is within reasonable agreement with our observed abundance, although is slightly higher than our observed value. For HE 1429-0551, our findings support the scenario via mass transfer by a primary companion during its thermally-pulsing phase. Our estimated upper limit in HE 1305+0007, along with data from the literature, shows large discrepancies compared with AGB models. The discrepancy is principally due to the simultaneous s- and r-process element enhancements which the model struggles to reproduce. 12 pages, 5 Figures -- Accepted in MNRAS

  • Open Access
    Authors: 
    Sijie Yu; James S. Bullock; Andrew Wetzel; Robyn E. Sanderson; Andrew S. Graus; Michael Boylan-Kolchin; Anna Nierenberg; Michael Y. Grudić; Philip F. Hopkins; Dušan Kereš; +1 more
    Publisher: Oxford University Press (OUP)
    Country: United States

    We study stellar-halo formation using six Milky Way-mass galaxies in FIRE-2 cosmological zoom simulations. We find that $5-40\%$ of the outer ($50-300$ kpc) stellar halo in each system consists of $\textit{in-situ}$ stars that were born in outflows from the main galaxy. Outflow stars originate from gas accelerated by super-bubble winds, which can be compressed, cool, and form co-moving stars. The majority of these stars remain bound to the halo and fall back with orbital properties similar to the rest of the stellar halo at $z=0$.In the outer halo, outflow stars are more spatially homogeneous, metal rich, and alpha-element-enhanced than the accreted stellar halo. At the solar location, up to $\sim 10 \%$ of our kinematically-identified halo stars were born in outflows; the fraction rises to as high as $\sim 40\%$ for the most metal-rich local halo stars ([Fe/H] $> -0.5$). We conclude that the Milky Way stellar halo could contain local counterparts to stars that are observed to form in molecular outflows in distant galaxies. Searches for such a population may provide a new, near-field approach to constraining feedback and outflow physics. A stellar halo contribution from outflows is a phase-reversal of the classic halo formation scenario of Eggen, Lynden-Bell $\&$ Sandange, who suggested that halo stars formed in rapidly $\textit{infalling}$ gas clouds. Stellar outflows may be observable in direct imaging of external galaxies and could provide a source for metal-rich, extreme velocity stars in the Milky Way. 19 pages, 20 figures, submitted to MNRAS

  • Open Access
    Authors: 
    Cora Uhlemann; Sandrine Codis; C. Pichon; Francis Bernardeau; Paulo H. F. Reimberg;
    Publisher: Oxford University Press (OUP)
    Country: France

    We present a first principle approach to obtain analytical predictions for spherically-averaged cosmic densities in the mildly non-linear regime that go well beyond what is usually achieved by standard perturbation theory. A large deviation principle allows us to compute the leading-order cumulants of average densities in concentric cells. In this symmetry, the spherical collapse model leads to cumulant generating functions that are robust for finite variances and free of critical points when logarithmic density transformations are implemented. They yield in turn accurate density probability distribution functions (PDFs) from a straightforward saddle-point approximation valid for all density values. Based on this easy-to-implement modification, explicit analytic formulas for the evaluation of the one- and two-cell PDF are provided. The theoretical predictions obtained for the PDFs are accurate to a few percent compared to the numerical integration, regardless of the density under consideration and in excellent agreement with N-body simulations for a wide range of densities. This formalism should prove valuable for accurately probing the quasi-linear scales of low redshift surveys for arbitrary primordial power spectra. 13 pages, 11 figures, minor corrections and added references, accepted for publication in MNRAS