اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدNew Surface Brightness Fluctuations Spectroscopic Technique: NGC4449 and its Stellar Tidal Stream
77
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present a new spectroscopic technique based in part on targeting the upward fluctuations of the surface brightness for studying the internal stellar kinematics and metallicities of low surface brightness galaxies and streams beyond the Local Group. The distance to these systems makes them unsuitable for targeting individual red giant branch (RGB) stars (tip of RGB at $Igtrsim24$~mag) and their surface brightness is too low ($mu_rgtrsim 25$~mag~arcsec$^{-2}$) for integrated light spectroscopic measurements. This technique overcomes these two problems by targeting individual objects that are brighter than the tip of the RGB. We apply this technique to the star-forming dwarf galaxy NGC 4449 and its stellar stream. We use Keck/DEIMOS data to measure the line-of-sight radial velocity out to $sim7$~kpc in the East side of the galaxy and $sim8$~kpc along the stream. We find that the two systems are likely gravitationally bound to each other and have heliocentric radial velocities of $227.3pm10.7$~km/s and $225.8pm16.0$~km/s, respectively. Neither the stream nor the near half of the galaxy shows a significant velocity gradient. We estimate the stellar metallicity of the stream based on the equivalent width of its Calcium triplet lines and find [Fe/H]~$=-1.37pm0.41$, which is consistent with the metallicity-luminosity relation for Local Group dwarf galaxies. Whether the streams progenitor was moderately or severely stripped cannot be constrained with this metallicity uncertainty. We demonstrate that this new technique can be used to measure the kinematics and (possibly) the metallicity of the numerous faint satellites and stellar streams in the halos of nearby ($sim 4$~Mpc) galaxies.
قيم البحث
اقرأ أيضاً
We examine the use of surface brightness fluctuations (SBF) for both stellar population and distance studies. New V-band SBF data are reported for five Fornax cluster galaxies and combined with literature data to define a new V-band SBF distance indi
cator. We use new stellar population models, based on the latest Padua isochrones transformed empirically to the observational plane, to predict SBF magnitudes and integrated colours for a wide range of population ages and metallicities. We examine the sensitivity of the predictions to changes in the isochrones, transformations, and IMF. The new models reproduce the SBF data for globular clusters fairly well, especially if higher metallicity globulars are younger. The models also give a good match to the fluctuation colors of elliptical galaxies. In order to obtain theoretical calibrations of the SBF distance indicators, we combine our single-burst models into composite population models. These models reproduce the observed behavior of the SBF magnitudes as a function of stellar population parameters, including the steep colour dependence found for HST/WFPC2 F814W SBF data. Because the theoretical SBF calibrations are fairly sensitive to uncertain details of stellar evolution, the empirical calibrations are more secure. However, the sensitivity of SBF to these finer details potentially makes it a powerful constraint for stellar evolution and population synthesis. [abbridged]
Mergers and tidal interactions between massive galaxies and their dwarf satellites are a fundamental prediction of the Lambda-Cold Dark Matter cosmology. These events are thought to influence galaxy evolution throughout cosmic history and to provide
important observational diagnostics of structure formation. Stellar streams in the Local Group are spectacular evidence for satellite disruption at the present day. However, constructing a significant sample of tidal streams beyond our immediate cosmic neighborhood has proven a daunting observational challenge and their potential for deepening our understanding of galaxy formation has yet to be realized. Over the last decade, the Stellar Tidal Stream Survey has obtained deep, wide-field images of nearby Milky-Way analog galaxies with a network of robotic amateur telescopes, revealing for the first time an assortment of large-scale tidal structures in their halos. I discuss the main results of this project and future plans for performing dynamical studies of the discovered streams.
I present integrated colors and surface brightness fluctuation magnitudes in the mid-IR, derived from stellar population synthesis models that include the effects of the dusty envelopes around thermally pulsing asymptotic giant branch (TP-AGB) stars.
The models are based on the Bruzual & Charlot CB* isochrones; they are single-burst, range in age from a few Myr to 14 Gyr, and comprise metallicities between $Z$= 0.0001 and $Z$ = 0.04. I compare these models to mid-IR data of AGB stars and star clusters in the Magellanic Clouds, and study the effects of varying self-consistently the mass-loss rate, the stellar parameters, and the output spectra of the stars plus their dusty envelopes. I find that models with a higher than fiducial mass-loss rate are needed to fit the mid-IR colors of extreme single AGB stars in the Large Magellanic Cloud. Surface brightness fluctuation magnitudes are quite sensitive to metallicity for 4.5 um and longer wavelengths at all stellar population ages, and powerful diagnostics of mass-loss rate in the TP-AGB for intermediate-age populations, between 100 Myr and 2-3 Gyr.
We are using optical/IR surface brightness fluctuations (SBFs) to validate the latest stellar population synthesis models and to understand the stellar populations of ellipticals. Integrated light and spectra measure only the first moment of the stel
lar luminosity function (Sigma n_i * L_i). Since SBFs also depend on the second moment (Sigma n_i * L_i^2), they provide novel information, in particular about the reddest, most luminous RGB and AGB stars, which are the most difficult stars to model. SBFs can also provide useful new constraints on the age/metallicity of unresolved stellar populations in ellipticals. Finally, developing accurate stellar population models benefits several aspects of SBF distance measurements to galaxies.
The aim of this work is to explore the potential of Surface Brightness Fluctuations (SBF) for studying composite stellar populations (CSP). To do so, we have computed the standard (mean) and SBF spectra with E-MILES stellar population synthesis code.
We have created a set of models composed by different mass fractions of two single stellar populations (SSP), as a first approximation of a CSP scenario. With these models we present an ensemble of SBF colour-colour diagnostic diagrams that reveal different secondary populations depending on the bands used. For this work we focus on those colours capable of unveiling small fractions of metal-poor components in elliptical galaxies, which are dominated by old metal-rich stellar populations. We fit a set of synthetic models and a selection of nearby elliptical galaxies to our CSP models using both mean and SBF colours. We find that the results are highly improved and return small secondary components when mean and SBF values are applied simultaneously, instead of employing them separately or as a constraint. Finally, we explore the possibility of tracking chemical enrichment histories by including in the analysis a variety of SBF colours. For this purpose we present an example where, with two different SBF colour-colour diagrams, we untangle a small contribution of a young solar population and an old metal-poor component from an old solar principal population. The results we have found are promising, but limited by the available data. We highlight the urgent need for new, better and more consistent SBF observations.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
