The lines of HOC$^+$, HCO and CO$^+$ are considered good tracers of photon-dominated regions (PDRs) and X-ray dominated regions. We study these tracers towards regions of the Sgr B2 cloud selected to be affected by different heating mechanisms. We find the lowest values of the column density ratios of HCO$^+$ versus HOC$^+$, HCO and CO$^+$ in dense HII gas, where UV photons dominate the heating and chemistry of gas. HOC$^+$, HCO and CO$^+$ abundances and the above ratios are compared with those of chemical modeling, finding that high temperature chemistry, a cosmic-ray ionization rate of 10$^{-16}$ s$^{-1}$ and timescales $>$10$^{5.0}$ years explain well the HOC$^+$ abundances in quiescent Sgr B2 regions, while shocks are also needed to explain the highest HCO abundances derived for these regions. CO$^+$ is mainly formed in PDRs since the highest CO$^+$ abundances of $\sim$(6-10)$\times$10$^{-10}$ are found in HII regions with electron densities $>$540 cm$^{-3}$ and that CO$^+$ emission is undetected in quiescent gas. Between the ratios, the HCO$^+$/HCO ratio is sensitive to the electron density as it shows different values in dense and diffuse HII regions. We compare SiO J=2-1 emission maps of Sgr B2 with X-ray maps from 2004 and 2012. One known spot shown on the 2012 X-ray map is likely associated with molecular gas at velocities of 15-25 km s$^{-1}$. We also derive the X-ray ionization rate of $\sim$10$^{-19}$ s$^{-1}$ for Sgr B2 regions pervaded by X-rays in 2004, which is quite low to affect the chemistry of the molecular gas.
In recent years, organic molecules of increasing complexity have been found toward the prolific Galactic center source Sagittarius B2. We wish to explore the degree of complexity that the interstellar chemistry can reach in star-forming regions. We carried out a complete line survey of the hot cores Sgr B2(N) and (M) with the IRAM 30 m telescope in the 3 mm range. We analyzed this spectral survey in the LTE approximation. We modeled the emission of all known molecules simultaneously, which allows us to search for less abundant, more complex molecules. We compared the derived column densities w…
We present abundances of C, O, Ti, and Fe for eleven M-giant stars in the trailing tidal arm of the Sagittarius dwarf (Sgr). The abundances were derived by comparing synthetic spectra with high-resolution infrared spectra obtained with the Phoenix spectrograph on the Gemini South telescope. The targeted stars are drawn from two regions of the Sgr trailing arm separated by 66 degrees (5 stars) and 132 degrees (6 stars) from the main body of Sgr. The trailing arm provides a more direct diagnostic of the chemical evolution of Sgr compared to the extensively phase-mixed leading arm. Within our res…
Using mm-wavelength data from ALMA, the EMoCA spectral line survey revealed the presence of both the straight-chain and branched forms of propyl cyanide (C$_3$H$_7$CN) toward the Galactic Center star-forming source Sgr B2(N2). This was the first interstellar detection of a branched aliphatic molecule. Through computational methods, we seek to explain the observed $i$:$n$ ratio for propyl cyanide, and to predict the abundances of the four different forms of the homologous nitrile, butyl cyanide (C$_4$H$_9$CN). We also investigate whether other molecules will show a similar degree of branching, …
The interstellar region within the few central parsecs around the super-massive black hole, Sgr A* at the very Galactic center is composed by a number of overlapping molecular structures which are subject to one of the most hostile physical environments in the Galaxy. We present high resolution (4"x3"~0.16x0.11 pc) interferometric observations of CN, 13CN, H2CO, SiO, c-C3H2 and HC3N emission at 1.3 mm towards the central ~4 pc of the Galactic center region. Strong differences are observed in the distribution of the different molecules. The UV resistant species CN, the only species tracing all …
We present three-dimensional kinematics of Sagittarius (Sgr) trailing tidal debris in six fields located 70-130 degrees along the stream from the Sgr dwarf galaxy core. The data are from our proper-motion (PM) survey of Kapteyn's Selected Areas, in which we have measured accurate PMs to faint magnitudes in 40x40 arcmin fields evenly spaced across the sky. The radial velocity (RV) signature of Sgr has been identified among our follow-up spectroscopic data in four of the six fields and combined with mean PMs of spectroscopically-confirmed members to derive space motions of Sgr debris based on 15…
The 1-50 GHz GBT PRIMOS data contains ~50 molecular absorption lines observed in diffuse and translucent clouds located in the Galactic Center, Bar, and spiral arms in the line-of-sight to Sgr B2(N). We measure the column densities and estimate abundances, relative to H2, of 11 molecules and additional isotopologues. We use absorption by optically thin transitions of c-C3H2 to estimate the N(H2), and argue that this method is preferable to more commonly used methods. We discuss the kinematic structure and abundance patterns of small molecules including the sulfur-bearing species CS, SO, CCS, H…
From molecular clouds to protoplanetary disks, non-ideal magnetic effects are important in many astrophysical environments. Indeed, in star and disk formation processes, it has become clear that these effects are critical to the evolution of the system. The efficacy of non-ideal effects are, however, determined by the complex interplay between magnetic fields, ionising radiation, cosmic rays, microphysics, and chemistry. In order to understand these key microphysical parameters, we present a one-dimensional non-ideal magnetohydrodynamics code and apply it to a model of a time-dependent, obliqu…
Sgr A* exhibits flaring in the infrared several times each day, occasionally accompanied by flaring in X-rays. The infrared flares are believed to arise through synchrotron emission from a transient population of accelerated electrons. The X-ray flaring has been interpreted as self-synchrotron-compton, inverse compton, or synchrotron emission associated with the transient electrons. Here I consider the upscattering of infrared flare photons by relativistic thermal electrons in the accretion flow around Sgr A*. Typical profiles of electron density and temperature in the accretion flow are adopt…
From chemical abundance analysis of stars in the Sagittarius dwarf spheroidal galaxy (Sgr), we conclude that the alpha-element deficiencies cannot be due to the Type Ia supernova (SNIa) time-delay scenario of Tinsley (1979). Instead, the evidence points to low [alpha/Fe] ratios resulting from an initial mass function (IMF) deficient in the highest mass stars. The critical evidence is the 0.4 dex deficiency of [O/Fe], [Mg/Fe] and other hydrostatic elements, contrasting with the normal trend of r-process [Eu/Fe]r with [Fe/H]. Supporting evidence comes from the hydrostatic element (O, Mg, Na, Al,…
As the number of complex organic molecules (COMs) detected in the interstellar medium increases, it becomes important to place meaningful constraints on the formation pathways of these species. The molecular cloud SgrB2(N) is host to several hot molecular cores in the early stage of star formation, where a great variety of COMs are detected in the gas phase. Because of its exposure to the extreme conditions of the the Galactic center region, SgrB2(N) is one of the best targets to study the impact of environmental conditions on the production of COMs. Our main goal is to characterize the physic…
We have selelcted 556 Red Horizontal Branch (RHB) stars along the streams of the Sagittarius dwarf galaxy (Sgr) from SDSS DR7 spectroscopic data using a theoretical model. The metallicity and α-elements distributions are investigated for stars in the Sgr streams and for Galactic stars at the same locations. We find that the Sgr stars have two peaks in the metallicity distribution while the Galactic stars have a more prominent metal-poor peak. Meanwhile, [α/Fe] ratios of the Sgr stars are lower than those of the Galactic stars. Among the Sgr stars, we find a difference in the metallicity distri…
In recent times, large organic molecules of exceptional complexity have been found in diverse regions of the interstellar medium. In this context, we aim to provide accurate frequencies of the ground vibrational state of two key aliphatic aldehydes, n-butanal and its branched-chain isomer, i-butanal, to enable their eventual detection in the interstellar medium. We employ a frequency modulation millimeter-wave absorption spectrometer to measure the rotational features of n- and i-butanal. We use the spectral line survey ReMoCA performed with the Atacama Large Millimeter/submillimeter Array to …
We investigated the emission of K$α$ iron line from the massive molecular clouds in the Galactic center (GC). We assume that at present the total flux of this emission consists of time variable component generated by primary X-ray photons ejected by Sagittarius A$^\ast$ (Sgr A$^\ast$) in the past and a relatively weak quasi-stationary component excited by impact of protons which were generated by star accretion onto the central black hole. The level of background emission was estimated from a rise of the 6.4 keV line intensity in the direction of several molecular clouds, that we interpreted a…
We present astrochemical photo-dissociation region models in which cosmic ray attenuation has been fully coupled to the chemical evolution of the gas. We model the astrochemical impact of cosmic rays, including those accelerated by protostellar accretion shocks, on molecular clouds hosting protoclusters. Our models with embedded protostars reproduce observed ionization rates. We study the imprint of cosmic ray attenuation on ions for models with different surface cosmic ray spectra and different star formation efficiencies. We find that abundances, particularly ions, are sensitive to the treat…
The Galactic Center (GC) has been long known to host gamma-ray emission detected to >10 TeV. HESS data now points to two plausible origins: the supermassive black hole (perhaps with >PeV cosmic rays and neutrinos) or high-energy electrons from the putative X-ray pulsar wind nebula G359.95-0.04 observed by Chandra and NuSTAR. We show that if the magnetic field experienced by PWN electrons is near the several mG ambient field strength suggested by radio observations of the nearby GC magnetar SGR J1745-29, synchrotron losses constrain the TeV gamma-ray output to be far below the data. Accounting …
Being one of the most abundant atomic/molecular species observed in dense molecular gas, atomic carbon ($\mathrm{C}^0$) is a potential good tracer of molecular gas mass in many chemical/physical environments, though the $\mathrm{C^0}$ abundance variation outside the Galactic disk region is yet to be fully known. This paper presents a wide-field 500 GHz [CI] map of the Galactic central molecular zone (CMZ) obtained with the ASTE 10-m telescope. Principal component analysis and non-LTE multi-transition analysis have shown that the [CI] emission predominantly originates from the low-excitation ga…
Radiatively inefficient accretion flows (RIAFs) in low-luminosity active galactic nuclei (LLAGNs) have been suggested as cosmic-ray and neutrino sources that may largely contribute to the observed diffuse neutrino intensity. We show that this scenario naturally predicts hadronic multi-TeV gamma-ray excesses around Galactic centers. The protons accelerated in the RIAF in Sagittarius A$^*$ (Sgr A$^*$) escape and interact with dense molecular gas surrounding Sgr A$^*$, which is known as the central molecular zone (CMZ), and produce gamma rays as well as neutrinos. Based on a theoretical model tha…
We observed OH, H$_2$O, HN$_3$, C$^{18}$O, and C$_I$ towards the +50 km/s cloud (M-0.02-0.07), the CND and the +20 km/s (M-0.13-0.08) cloud in the Sgr A complex with the VLA, Odin and SEST. Strong OH absorption, H$_2$O emission and absorption lines were seen at all three positions. Strong C$^{18}$O emissions were seen towards the +50 and +20 km/s clouds. The CND is rich in H$_2$O and OH, and these abundances are considerably higher than in the surrounding clouds, indicating that shocks, star formation and clump collisions prevail in those objects. A comparison with the literature reveals that …
Strong iron fluorescence at 6.4 keV and hard-X-ray emissions from giant molecular clouds in the Galactic center region have been interpreted as reflections of a past outburst of the Sgr A* supermassive black hole. Careful treatment of multiple interactions of photons in a complicated geometry is essential to modeling the reprocessed emissions from the dense clouds. We develop a new calculation framework of X-ray reflection from molecular clouds based on Monte Carlo simulations for accurate interpretation of high-quality observational data. By utilizing this simulation framework, we present the…
Cosmic rays are crucial for the chemistry of molecular clouds and their evolution. They provide essential ionizations, dissociations, heating and energy to the cold, dense cores. As cosmic rays pierce through the clouds they are attenuated and lose energy, which leads to a dependency on the column density of a system. The detailed effects these particles have on the central regions still needs to be fully understood. Here, we revisit how cosmic rays are treated in the UCLCHEM chemical modeling code by including both ionization rate and H2 dissociation rate dependencies alongside the production…
The current paradigm of Galactic Center (GC) gas motions and star formation envisions sequential star formation in streams of gas as they pass near the supermassive black hole, Sgr A*. This is based on the relative positions of dense molecular clouds, the very young star-forming region Sgr B2, the much older region Sgr C, and the several Myr old Arches and Quintuplet Clusters. Because Sgr B1 is found with Sgr B2 in a common envelope of molecular gas and far-infrared emission, the two sources are thought to be physically related, even though there are indicators of a significantly greater age f…
The Galaxy's supermassive black hole, Sgr A*, produces an outburst of infrared radiation about once every 6 hours, sometimes accompanied by an even more energetic flurry of X-rays. The NIR photons are produced by nonthermal synchrotron processes, but we still don't completely understand where or why these flares originate, nor exactly how the X-rays are emitted. The power-law electrons radiating the infrared light may be partially cooled, so the distribution may be a broken power law with a ("cooling break") transition frequency. In addition, the emission region appears to be rather compact, p…
We present a new methodology to derive the positions of the Sgr B molecular clouds (MCs) along the line of sight, as an application study of the Galactic center diffuse X-rays (GCDX). The GCDX is composed of hot plasma emission of about 7 keV and 1 keV temperatures, and non-thermal continuum emission including the 6.4 keV line from neutral irons. The former, the Galactic center plasma emission (GCPE), is uniformly distributed over 1 degree in longitude, while the latter is clumpy emission produced by Thomson scattering and fluorescence from MCs irradiated by external X-rays (the X-ray reflecti…
The Sagittarius B2 (Sgr B2) molecular cloud complex is an X-ray reflection nebula whose total emissions have continued to decrease since 2001 as it reprocesses one or more past energetic outbursts from the supermassive black hole Sagittarius A*. The X-ray reflection model explains the observed time variability and provides a window into the luminous evolutionary history of our nearest supermassive black hole. In light of evidence of elevated cosmic particle populations in the Galactic Center, X-rays from Sgr B2 are also of interest as a probe of low-energy (sub-GeV) cosmic rays, which may be r…
Supernova remnants (SNRs) have commonly been considered as a source of the observed PeV cosmic rays (CRs) or a Galactic PeV particle accelerator ("Pevatron"). In this work, we study Sagittarius A* (Sgr A*), which is the low-luminosity active galactic nucleus of the Milky Way Galaxy, as another possible canditate of the Pevatron, because it sometimes became very active in the past. We assume that a large number of PeV CRs were injected by Sgr A* at the outburst about 10^7 yr ago when the Fermi bubbles were created. We constrain the diffusion coefficient for the CRs in the Galactic halo on the c…
Cosmic rays pervade the Galaxy and are thought to be accelerated in supernova shocks. The interaction of cosmic rays with dense interstellar matter has two important effects: 1) high energy (>1 GeV) protons produce γ-rays by π0-meson decay; 2) low energy (< 1 GeV) cosmic rays (protons and electrons) ionize the gas. We present here new observations towards a molecular cloud close to the W51C supernova remnant and associated with a recently discovered TeV γ-ray source. Our observations show that the cloud ionization degree is highly enhanced, implying a cosmic ray ionization rate ~ 10-15 s-1, i.…
We report serendipitous detections of line emission with ALMA in band 3, 6, and 7 in the central parsec of the Galactic center at an up to now highest resolution (<0.7''). Among the highlights are the very first and highly resolved images of sub-mm molecular emission of CS, H13CO+, HC3N, SiO, SO, C2H, and CH3OH in the immediate vicinity (~1'' in projection) of Sgr A* and in the circumnuclear disk (CND). The central association (CA) of molecular clouds shows three times higher CS/X (X: any other observed molecule) luminosity ratios than the CND suggesting a combination of higher excitation - by…
It has been indicated that low-luminosity active galactic nuclei (LLAGNs) are accelerating high-energy cosmic-ray (CR) protons in their radiatively inefficient accretion flows (RIAFs). If this is the case, Sagittarius A* (Sgr A*) should also be generating CR protons, because Sgr A* is a LLAGN. Based on this scenario, we calculate a production rate of CR protons in Sgr A* and their diffusion in the central molecular zone (CMZ) around Sgr A*. The CR protons diffusing in the CMZ create gamma-rays through pp interaction. We show that the gamma-ray luminosity and spectrum are consistent with observ…
The nature of the Triangulum-Andromeda (TriAnd) system has been debated since the discovery of this distant, low-latitude Milky Way (MW) overdensity more than a decade ago. Explanations for its origin are either as a halo substructure from the disruption of a dwarf galaxy or a distant extension of the Galactic disk. We test these hypotheses using chemical abundances of a dozen TriAnd members from the Sloan Digital Sky Survey's 14th Data Release of Apache Point Observatory Galactic Evolution Experiment (APOGEE) data to compare to APOGEE abundances of stars with similar metallicity from both the…
We summarize recent observations and modeling of the brightest Sgr A* flare to be observed simultaneously in (near)-infrared and X-rays to date. Trying to explain the spectral characteristics of this flare through inverse Compton mechanisms implies physical parameters that are unrealistic for Sgr A*. Instead, a "cooling break" synchrotron model provides a more feasible explanation for the X-ray emission. In a magnetic field of about 5-30 Gauss the X-ray emitting electrons cool very quickly on the typical dynamical timescale while the NIR-emitting electrons cool more slowly. This produces a spe…
Sgr A*, the supermassive black hole (SMBH) in our Galaxy, is dormant today, but it should have gone through multiple gas-accretion episodes in the past billions of years to grow to its current mass of $4\times10^6\,M_\odot$. Each episode temporarily ignites the SMBH and turns the Galactic Center into an active galactic nucleus (AGN). Recently, we showed that the AGN could produce large amount of hard X-rays that can penetrate the dense interstellar medium in the Galactic plane. Here we further study the impact of the X-rays on the molecular chemistry in our Galaxy. We use a chemical reaction n…
We use the gas-grain chemistry code UCLCHEM to explore the impact of cosmic-ray feedback on the chemistry of circumstellar disks. We model the attenuation and energy losses of the cosmic-rays as they propagate outwards from the star and also consider ionization due to stellar radiation and radionuclides. For accretion rates typical of young stars, $\dot M_* \sim 10^{-9}-10^{-6}$ M_\odot yr$^{-1}$, we show that cosmic rays accelerated by the stellar accretion shock produce a cosmic-ray ionization rate at the disk surface $ζ\gtrsim 10^{-15}$ s$^{-1}$, at least an order of magnitude higher than t…
In cold core of dark molecular clouds, where the UV radiation from external sources is strongly attenuated, cosmic rays can induce chemical reactions on the surface of ice-covered grains promoting the ejection of the processed material to the gas phase. We report the positive and negative secondary ion emission from pure CH3CN, C2H3CN and i-C3H7CN ices due to the bombardment of heavy ions (252Cf fission fragments), simulating the incidence of cosmic rays onto icy surfaces. The secondary ions emitted from each sample were analysed by time-of-flight mass spectrometry (TOF-MS), using Plasma Desor…
We present the result of a study of the X-ray emission from the Galactic Centre Molecular Clouds (MC), within 15 arcmin from Sgr A*. We use XMM-Newton data spanning about 8 years. We observe an apparent super-luminal motion of a light front illuminating a MC. This might be due to a source outside the MC (such as Sgr A* or a bright and long outburst of a X-ray binary), while it can not be due to low energy cosmic rays or a source located inside the cloud. We also observe a decrease of the X-ray emission from G0.11-0.11, behaviour similar to the one of Sgr B2. The line intensities, clouds dimens…
We present high-resolution spectroscopic measurements of the abundances of titanium (Ti), yttrium (Y) and lanthanum (La) for M giant candidates of the Sagittarius (Sgr) dwarf spheroidal (dSph) + tidal tail system pre-selected on the basis of position and radial velocity. The majority of these stars show peculiar abundance patterns compared to those of nominal Milky Way (MW) stars. The overall [Ti/Fe], [Y/Fe], [La/Fe] and [La/Y] patterns with [Fe/H] of the Sgr stream plus Sgr core do resemble those seen in the Large Magellanic Cloud (LMC) and other dSphs, only shifted [Fe/H] by ~+0.4 from the L…
Sgr B2 is a well-known star forming molecular cloud complex in the Galactic center region showing evidence of high energy activity as traced by the K$α$ neutral FeI line at 6.4 keV, as well as GeV and TeV $γ$-ray emission. Here we present VLA and GMRT observations with respective resolutions of $\approx3.5"\times1.2"$ and 25$"\times25"$ and report the detection of an OH(1720 MHz) maser, with no accompanying OH 1665, 1667 and 1612 MHz maser emission. The maser coincides with a 150 MHz nonthermal radio source in Sgr B2(M). This rare class of OH(1720 MHz) masers or the so-called supernova remnant…
We present the result of a study of the X-ray emission from the Galactic Centre (GC) Molecular Clouds (MC) within 15 arcmin from Sgr A*. We use XMM-Newton data (about 1.2 Ms of observation time) spanning about 8 years. The MC spectra show all the features characteristic of reflection: i) intense Fe Kalpha, with EW of about 0.7-1 keV, and the associated Kbeta line; ii) flat power law continuum and iii) a significant Fe K edge (tau~0.1-0.3). The diffuse low ionisation Fe K emission follows the MC distribution, nevertheless not all MC are Fe K emitters. The long baseline monitoring allows the cha…
The tidal disruption of the Sagittarius dwarf Spheroidal galaxy (Sgr dSph) is producing the most prominent substructure in the Milky Way (MW) halo, the Sagittarius Stream. Aside from field stars, the Sgr dSph is suspected to have lost a number of globular clusters (GC). Many Galactic GC are suspected to have originated in the Sgr dSph. While for some candidates an origin in the Sgr dSph has been confirmed due to chemical similarities, others exist whose chemical composition has never been investigated. NGC 5053 and NGC 5634 are two among these scarcely studied Sgr dSph candidate-member cluster…
