Faint Photometry of Edge-on Spiral Galaxies: A Search for Massive Halos

Upper limits have been set to the luminosity from the massive halos of three late-type edge-on spiral galaxies: NGC 2683 (Sb), NGC 4244 (Scd), and NGC 5907 (Sc). The limits resulted from simultaneous photometry in the visual (V) and 2.2μm (K) photometric bands which is sensitive to both luminosity and color changes along the minor axes of the three galaxies. The 3σ lower limits to the mass-to-light ratios for the halo of NGC 5907 are the largest ever recorded: M/Lv > 2000 and M/Lk > 64 in solar units. Since K band M/L for M-dwarf stars lying just above the hydrogen-burning limit is about 35, the results virtually eliminate the possibility that hydrogen-burning stars comprise more than a fraction of the halo masses. If the halos contain a more realistic spectrum of stellar masses, for example Population II, the visual band measurements imply that these stars account for less than one percent of the halo mass. Similar limits were obtained for NGC 4244 and NGC 2683. Variations of the V-K colors along and perpendicular to the disks show no sign of population changes toward redder objects at large galactocentric radii.

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Mass-to-Light Ratios of Spiral Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900150107 ◽

1987 ◽

Vol 117 ◽

pp. 138-138

Author(s):

J. Patricia Vader

Keyword(s):

Theoretical Model ◽

Spiral Galaxies ◽

Evolution Of Galaxies ◽

Large Structures ◽

Model Predictions ◽

Formation And Evolution ◽

Color Bias ◽

Massive Halos ◽

Stellar Masses ◽

The Universe

Mass-to-light ratios M/LH−0.5 and M/LB are plotted against color B-H−0.5 in Fig. 1 for 82 nearby spirals from the catalog of Aaronson et al. (1982, Ap. J. Suppl. 50, 241), with BT magnitudes from the RC2, |b| > 20°, 45° ≤ i ≤ 80°, and HI mass estimates. Total masses and infrared H−0.5 magnitudes are measured within the blue isophotal radii R25 and R25/3 respectively, which depend on galaxy color. This color bias is corrected for by replacing R25 by R'25, the radius a galaxy would have at a standard color B-H−0.5 = 2.17. Stellar masses M* and LHC luminosities within R'25 are obtained by substracting twice the HI mass and by extrapolation, respectively. Corrected ratios M*/LHC and M*/LB versus corrected color B-HC are shown in Fig. 1 together with theoretical model predictions. The corrected observed ratios are systematically larger for bluer galaxies than predicted so that bluer spirals seem to have relatively more massive halos, in agreement with earlier results (Tinsley, B.M. 1981 M.N.R.A.S. 194, 63; Vader, J. P. 1984, in Formation and Evolution of Galaxies and Large Structures in the Universe, eds. J. Audouze and J. T. Thanh Van, p. 227).

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Exploring the possibility of Peter Pan discs across stellar mass

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab2523 ◽

2021 ◽

Author(s):

Martijn J C Wilhelm ◽

Simon Portegies Zwart

Keyword(s):

Mass Loss ◽

Stellar Mass ◽

Radiation Environment ◽

Peter Pan ◽

Dwarf Stars ◽

Star Mass ◽

Stellar Masses ◽

M Dwarf Stars ◽

M Dwarf ◽

Host Stars

Abstract Recently, several accreting M dwarf stars have been discovered with ages far exceeding the typical protoplanetary disc lifetime. These ‘Peter Pan discs’ can be explained as primordial discs that evolve in a low-radiation environment. The persistently low masses of the host stars raise the question whether primordial discs can survive up to these ages around stars of higher mass. In this work we explore the way in which different mass loss processes in protoplanetary discs limit their maximum lifetimes, and how this depends on host star mass. We find that stars with masses ≲ 0.6 M⊙ can retain primordial discs for ∼50 Myr. At stellar masses ≳ 0.8 M⊙, the maximum disc lifetime decreases strongly to below 50 Myr due to relatively more efficient accretion and photoevaporation by the host star. Lifetimes up to 15 Myr are still possible for all host star masses up to ∼2 M⊙. For host star masses between 0.6 and 0.8 M⊙, accretion ceases and an inner gap forms before 50 Myr in our models. Observations suggest that such a configuration is rapidly dispersed. We conclude that Peter Pan discs can only occur around M dwarf stars.

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Planet formation around M dwarfs via disc instability

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936954 ◽

2020 ◽

Vol 633 ◽

pp. A116

Author(s):

Anthony Mercer ◽

Dimitris Stamatellos

Keyword(s):

Planet Formation ◽

M Dwarfs ◽

Low Mass Stars ◽

Dwarf Stars ◽

Low Mass ◽

Protostellar Discs ◽

Stellar Masses ◽

M Dwarf Stars ◽

Core Accretion ◽

M Dwarf

Context. Around 30 per cent of the observed exoplanets that orbit M dwarf stars are gas giants that are more massive than Jupiter. These planets are prime candidates for formation by disc instability. Aims. We want to determine the conditions for disc fragmentation around M dwarfs and the properties of the planets that are formed by disc instability. Methods. We performed hydrodynamic simulations of M dwarf protostellar discs in order to determine the minimum disc mass required for gravitational fragmentation to occur. Different stellar masses, disc radii, and metallicities were considered. The mass of each protostellar disc was steadily increased until the disc fragmented and a protoplanet was formed. Results. We find that a disc-to-star mass ratio between ~0.3 and ~0.6 is required for fragmentation to happen. The minimum mass at which a disc fragment increases with the stellar mass and the disc size. Metallicity does not significantly affect the minimum disc fragmentation mass but high metallicity may suppress fragmentation. Protoplanets form quickly (within a few thousand years) at distances around ~50 AU from the host star, and they are initially very hot; their centres have temperatures similar to the ones expected at the accretion shocks around planets formed by core accretion (up to 12 000 K). The final properties of these planets (e.g. mass and orbital radius) are determined through long-term disc-planet or planet–planet interactions. Conclusions. Disc instability is a plausible way to form gas giant planets around M dwarfs provided that discs have at least 30% the mass of their host stars during the initial stages of their formation. Future observations of massive M dwarf discs or planets around very young M dwarfs are required to establish the importance of disc instability for planet formation around low-mass stars.

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Cosmic-Ray Driven Outflows to Mpc Scales from L* Galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3690 ◽

2020 ◽

Author(s):

Philip F Hopkins ◽

T K Chan ◽

Suoqing Ji ◽

Cameron B Hummels ◽

Dušan Kereš ◽

...

Keyword(s):

Cosmic Ray ◽

Plane Layer ◽

Equilibrium Density ◽

Pressure Gradients ◽

Low Velocity ◽

Star Forming ◽

Stellar Feedback ◽

Massive Halos ◽

Halo Masses

Abstract We study the effects of cosmic rays (CRs) on outflows from star-forming galaxies in the circum and inter-galactic medium (CGM/IGM), in high-resolution, fully-cosmological FIRE-2 simulations (accounting for mechanical and radiative stellar feedback, magnetic fields, anisotropic conduction/viscosity/CR diffusion and streaming, and CR losses). We showed previously that massive (Mhalo ≳ 1011 M⊙), low-redshift (z ≲ 1 − 2) halos can have CR pressure dominate over thermal CGM pressure and balance gravity, giving rise to a cooler CGM with an equilibrium density profile. This dramatically alters outflows. Absent CRs, high gas thermal pressure in massive halos “traps” galactic outflows near the disk, so they recycle. With CRs injected in supernovae as modeled here, the low-pressure halo allows “escape” and CR pressure gradients continuously accelerate this material well into the IGM in “fast” outflows, while lower-density gas at large radii is accelerated in-situ into “slow” outflows that extend to >Mpc scales. CGM/IGM outflow morphologies are radically altered: they become mostly volume-filling (with inflow in a thin mid-plane layer) and coherently biconical from the disk to >Mpc. The CR-driven outflows are primarily cool (T ∼ 105 K) and low-velocity. All of these effects weaken and eventually vanish at lower halo masses (≲ 1011 M⊙) or higher redshifts (z ≳ 1 − 2), reflecting the ratio of CR to thermal+gravitational pressure in the outer halo. We present a simple analytic model which explains all of the above phenomena. We caution that these predictions may depend on uncertain CR transport physics.

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Bar rejuvenation in S0 galaxies?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1387 ◽

2020 ◽

Vol 495 (4) ◽

pp. 4548-4556

Author(s):

Sudhanshu Barway ◽

Kanak Saha

Keyword(s):

Star Formation ◽

Spiral Galaxies ◽

Theoretical Studies ◽

Tidal Interactions ◽

Colour Measurements ◽

Induce Star Formation ◽

Minor Mergers ◽

Stellar Masses ◽

S0 Galaxies ◽

Intermediate Density

ABSTRACT Based on the colour measurements from a multiband, multicomponent 2D decompositions of S0 and spiral galaxies using SDSS images, we found that bars are bluer in S0 galaxies compared to the spiral galaxies. Most of the S0s in our sample have stellar masses ∼L* galaxies. The environment might have played an important role as most of the S0s with bluer bars are in the intermediate-density environment. The possibility of minor mergers and tidal interactions that occurs frequently in the intermediate-density environment might have caused either a bar to form and/or induce star formation in the barred region of S0 galaxies. The underlying discs show the usual behaviour being redder in S0s compared to spiral galaxies while the bulges are red and old for both S0 and spiral galaxies. The finding of bluer bars in S0 galaxies is a puzzling issue and poses an interesting question at numerical and theoretical studies most of which shows that the bars are long-lived structures with old stellar populations.

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Properties of the circumgalactic medium in simulations compared to observations

Astronomy and Astrophysics ◽

10.1051/0004-6361/201628886 ◽

2018 ◽

Vol 609 ◽

pp. A66 ◽

Cited By ~ 3

Author(s):

R. E. G. Machado ◽

P. B. Tissera ◽

G. B. Lima Neto ◽

L. Sodré

Keyword(s):

Gas Phase ◽

Chemical Elements ◽

Star Forming ◽

Physical Conditions ◽

Cosmological Context ◽

Circumgalactic Medium ◽

Hydrodynamical Simulations ◽

Stellar Masses ◽

Lower Limits ◽

Supernova Feedback

Context. Galaxies are surrounded by extended gaseous halos that store significant fractions of chemical elements. These are syntethized by the stellar populations and later ejected into the circumgalactic medium (CGM) by different mechanism, of which supernova feedback is considered one of the most relevant. Aims. We aim to explore the properties of this metal reservoir surrounding star-forming galaxies in a cosmological context aiming to investigate the chemical loop between galaxies and their CGM, and the ability of the subgrid models to reproduce observational results. Methods. Using cosmological hydrodynamical simulations, we have analysed the gas-phase chemical contents of galaxies with stellar masses in the range 109−1011 M⊙. We estimated the fractions of metals stored in the different CGM phases, and the predicted O vi and Si iii column densities within the virial radius. Results. We find roughly 107 M⊙ of oxygen in the CGM of simulated galaxies having M⋆ ~ 1010 M⊙, in fair agreement with the lower limits imposed by observations. The Moxy is found to correlate with M⋆, at odds with current observational trends but in agreement with other numerical results. The estimated profiles of O vi column density reveal a substantial shortage of that ion, whereas Si iii, which probes the cool phase, is overpredicted. Nevertheless, the radial dependences of both ions follow the respective observed profiles. The analysis of the relative contributions of both ions from the hot, warm and cool phases suggests that the warm gas (105 K < T < 106 K) should be more abundant in order to bridge the mismatch with the observations, or alternatively, that more metals should be stored in this gas-phase. These discrepancies provide important information to improve the subgrid physics models. Our findings show clearly the importance of tracking more than one chemical element and the difficulty of simultaneously satisfying the observables that trace the circumgalactic gas at different physical conditions. Additionally, we find that the X-ray coronae around the simulated galaxies have luminosities and temperatures in decent agreement with the available observational estimates.

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The CARMENES search for exoplanets around M dwarfs

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038279 ◽

2020 ◽

Vol 640 ◽

pp. A52

Author(s):

B. Fuhrmeister ◽

S. Czesla ◽

L. Hildebrandt ◽

E. Nagel ◽

J. H. M. M. Schmitt ◽

...

Keyword(s):

Near Infrared ◽

Extreme Ultraviolet ◽

High Energy ◽

M Dwarfs ◽

Dwarf Stars ◽

Transmission Spectroscopy ◽

Solar Type ◽

Energy Irradiation ◽

Planetary Transmission ◽

M Dwarf Stars

The He I infrared (IR) triplet at 10 830 Å is known as an activity indicator in solar-type stars and has become a primary diagnostic in exoplanetary transmission spectroscopy. He I IR lines are a tracer of the stellar extreme-ultraviolet irradiation from the transition region and corona. We study the variability of the He I triplet lines in a spectral time series of 319 M dwarf stars that was obtained with the CARMENES high-resolution optical and near-infrared spectrograph at Calar Alto. We detect He I IR line variability in 18% of our sample stars, all of which show Hα in emission. Therefore, we find detectable He I variability in 78% of the sub-sample of stars with Hα emission. Detectable variability is strongly concentrated in the latest spectral sub-types, where the He I lines during quiescence are typically weak. The fraction of stars with detectable He I variation remains lower than 10% for stars earlier than M3.0 V, while it exceeds 30% for the later spectral sub-types. Flares are accompanied by particularly pronounced line variations, including strongly broadened lines with red and blue asymmetries. However, we also find evidence for enhanced He I absorption, which is potentially associated with increased high-energy irradiation levels at flare onset. Generally, He I and Hα line variations tend to be correlated, with Hα being the most sensitive indicator in terms of pseudo-equivalent width variation. This makes the He I triplet a favourable target for planetary transmission spectroscopy.

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Low Metallicity Galaxies at z ~ 0.7: Keys to the Origins of Metallicity Scaling Laws

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308025143 ◽

2008 ◽

Vol 4 (S255) ◽

pp. 397-401

Author(s):

David J. Rosario ◽

Carlos Hoyos ◽

David Koo ◽

Andrew Phillips

Keyword(s):

Star Formation ◽

Emission Line ◽

Galaxy Evolution ◽

Scaling Laws ◽

Temperature Sensitive ◽

Star Forming ◽

Low Metallicity ◽

Emission Line Galaxies ◽

Halo Masses ◽

Stellar Masses

AbstractWe present a study of remarkably luminous and unique dwarf galaxies at redshifts of 0.5 < z < 0.7, selected from the DEEP2 Galaxy Redshift survey by the presence of the temperature sensitive [OIII]λ4363 emission line. Measurements of this important auroral line, as well as other strong oxygen lines, allow us to estimate the integrated oxygen abundances of these galaxies accurately without being subject to the degeneracy inherent in the standard R23 system used by most studies. [O/H] estimates range between 1/5–1/10 of the solar value. Not surprisingly, these systems are exceedingly rare and hence represent a population that is not typically present in local surveys such as SDSS, or smaller volume deep surveys such as GOODS.Our low-metallicity galaxies exhibit many unprecedented characteristics. With B-band luminosities close to L*, thse dwarfs lie significantly away from the luminosity-metallicity relationships of both local and intermediate redshift star-forming galaxies. Using stellar masses determined from optical and NIR photometry, we show that they also deviate strongly from corresponding mass-metallicity relationships. Their specific star formation rates are high, implying a significant burst of recent star formation. A campaign of high resolution spectroscopic follow-up shows that our galaxies have dynamical properties similar to local HII and compact emission line galaxies, but mass-to-light ratios that are much higher than average star-forming dwarfs.The low metallicities, high specific star formation rates, and small halo masses of our galaxies mark them as lower redshift analogs of Lyman-Break galaxies, which, at z ~ 2 are evolving onto the metallicity sequence that we observe in the galaxy population of today. In this sense, these systems offer fundamental insights into the physical processes and regulatory mechanisms that drive galaxy evolution in that epoch of major star formation and stellar mass assembly.

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An Astrobiological Experiment to Explore the Habitability of Tidally Locked M-Dwarf Planets

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313012817 ◽

2012 ◽

Vol 8 (S293) ◽

pp. 192-196

Author(s):

Daniel Angerhausen ◽

Haley Sapers ◽

Eugenio Simoncini ◽

Stefanie Lutz ◽

Marcelo da Rosa Alexandre ◽

...

Keyword(s):

Academic Research ◽

Environmental Parameters ◽

Climate Simulation ◽

Habitable Zone ◽

Dwarf Stars ◽

Dwarf Planets ◽

Late Type Star ◽

M Dwarf Stars ◽

M Dwarf ◽

Simulation Chamber

AbstractWe present a summary of a three-year academic research proposal drafted during the Sao Paulo Advanced School of Astrobiology (SPASA) to prepare for upcoming observations of tidally locked planets orbiting M-dwarf stars. The primary experimental goal of the suggested research is to expose extremophiles from analogue environments to a modified space simulation chamber reproducing the environmental parameters of a tidally locked planet in the habitable zone of a late-type star. Here we focus on a description of the astronomical analysis used to define the parameters for this climate simulation.

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