Galaxy topics
Jets, accretion, outflows
Gamma ray burst (GRB)

	The Milky Way Galaxy: The Sun is moving around the Galactic center with a orbital period of about 2.3x10^8 yr. It also moves up and down relative to the plane of the Galaxy with an amplitude of 70 pc. (from Duley & Williams, 1984, Interstellar Chemistry, Harcourt Brace Jovanovich, publishers, chapter 1.2, page 2.) Basic physical parameters the Galaxy: Age: 1.2x10^10 yr diameter: 25 kpc thickness: 250 pc Mass: 1.4x10^11 Msun Overal density: 7x10^-24 g cm^-3 Sun's distance to the galactic center: 9 kpc (8.5 kpc) Sun's distance to the galactic plane: 0 Circular speed at the Sun's location: 250 km/s Mass density at the Sun's location: 1.4x10-23 g/cm (nH + nHe = 6+-0.6 cm^-3) Average interstellar H density at the Sun's location: 2x10^-24 g cm^-3 (1.2 cm^-3) Mean separation of stars in the solar neighbourhood: ~1 pc (from Duley & Williams, 1984, Interstellar Chemistry, Harcourt Brace Jovanovich, publishers, chapter 1.2)
	Neutrinos -- messengers in the Universe (from the colloquium talk by Dr. Lin Guey-Yin at ASIAA on ) Comparison of the direction of detected high energy cosmic ray (with energy E > 7.5 x 10^19 eV, direction uncertainty of 3.2 deg) with the spatial distribution of nearby AGNs (with distance D < 71 Mpc) showed that many of the c.r. are correlated with AGNs. There are three kinds of neutrinos: electron neutrino nu_e, muon neutrino nu_mu and pion neutrino nu_pi. Nu_mu and nu_pi are two eign states and a neutrino is usually oscilating between the two states. Neutrinos with higher energy have higher oscilation frequency and so shorter period. Nu_e is another eign state, so a neutrino can oscilate between nu_e and nu_mu, nu_pi as well. The neutrino oscilation explains the neutrino deficiency problem in both the Sun and the Cosmos.
	Evolution of merger rate for Field Galaxies & Brief Report of the RCS Meeting 2007 (from the lunch box talk by Dr. Bau-Ching Hsieh at ASIAA on Nov. 5, 2007) Their criteria of close galaxy pair: distance < 5-20 kpc; d z < 2.5 sigma_z; d M_Rc < 1 mag.
	How does galaxy morphology change. (from Dr Changbum Pack's colloquium talk at ASIAA on Nov. 28, 2007)  Morphology of galaxies (early type: E/S0 and late type: S/Irr) is correlated with colors and can be differentiated on the d[g-i]-[u-r] plot. Therefore, this plot is a useful tool to automatically classify the morphology type of a huge amount of galaxies. With the information of apparent position and redshift z, and criteria d Mr < 0.5, d V < 600/ 400 km/s, it is possible to find a nearest neighbor for each galaxy. They form a sample of galaxy pairs. Matter density around each galaxy also can be calculated from the 3D distribution of galaxies around it.  The probability to own an early type galaxy companion is found to be monotonically decreasing with pair distance (from about 0.8 to 0.0) for early type galaxies, while for late type galaxies, the probability has a maximum around the case in which the pair distance is close to virial radius.  Relation between morphology and pair distance: the galaxy morphology is controlled by star formation timescale ts and gravitational collapse timescale tc. For massive galaxies that usually form in high density environment, the ts/tc ratio is small, so that star formation proceeds fast and use up most of the gaseous material. Then the galaxy can not develope spiral structure but show up as an early type galaxy with most of it mass locked in stellar components. For low mass galaxies that usually form in low density environment, the ts/tc ratio is large, so that star formation proceeds very slowly and most matter still remain in gaseous phase. Then the galaxy will develope spiral and/or bar structures through hydrodynamic effect and show up as a late type galaxy with star formation activity. The distance between galaxy pairs reflects the density of the galaxy formation environment, and so the probability to find an early type companion galaxy is lower for larger pair distance (lower environment density). The lower probability at small pair distance (smaller than Virial radius) for the late type galaxies can be explained by mass transfer of gaseous material from the late type galaxies to their companion. (Part of these ideas were clarified through my personal discussions with Dr. Sandor Molnar.) Only 15% of galaxies (percentage in number of galaxies) exist in clusters, while the other 85% are field galaxies formed from filaments of matter in the universe. (from personal discussion with Dr. Sandor Molnar)
	Arp 220  This is a ULIRG (Ultra Luminous InfraRed Galaxy) with IR luminosity (between 8-1000mu) of 1.4x1012 Lo (Soifer et al., 1987). The distance is about 79.9 Mpc (Sanders et al., 2003). Arp 220 has two nuclei, separated by 1 arcsec (~390 pc). It's believed to be in the final evolutionary stage of a merger galaxy. Satoki observed high J CO transition mapping (CO J=6-5) of Arp 220 using the SMA. The two nuclei are marginally resolved in the CO 6-5 map. He argued that the two cores may have different dust temperatures. (Notes from Satoki Matsushita's SMA science talk on 11 Apr. 2007 in ASIAA)
	Cluster of galaxies are usually observable only in the 0.5-0.6 Rvir radius range (Rvir is the Virial radius of the cluster according to virial therom). (from Dr. Sandor M. Molnar's lunch box talk in ASIAA on Arp. 17, 2007).
	Baryon/total matter ratio in clusters of galaxies is found to be 0.168+-0.007 from observations. 22% of baryonic matter is missing in cluster of galaxies. (Cosmic baryonic ratio is 10%. ???) (from Dr. Sandor M. Molnar's lunch box talk in ASIAA on Arp. 17, 2007).
	SPH and AMR simulation shows that more baryonic matter exists in more extended region beyond observable regions (from Dr. Sandor M. Molnar's lunch box talk in ASIAA on Arp. 17, 2007). SPH means smooth partical hydrodynamic simulation; AMR means adaptive mesh refinement method.
	VIRGO software for hydrodynamic simulation of galaxy clusters. (See Bialek et al., 2001)
	In his lunch talk, Dr. Ananda Hota gave several galaxies or galaxy clusters that show super-winds, outflows, ram pressure stripping effects. Examples:         NGC 1482 -- super-wind;        NGC 6764 -- composite galaxy;        NGC 4438 -- outflow + ram pressure stripping effect;        Ho 124 -- a galaxy group with four members;        A1367  -- show a very long tails of 50-75 kpc long.
	X-ray cooling flow? (From the lunch talk by Jeremy Lim on 11th June, 2007 at ASIAA) Hot gas in galaxy clusters has very high temperature (107-108 K) and emits strong X ray. Galaxy clusters, such as Coma cluster and Perseus cluster, show strong X-ray emission peak at the center of the cluster. The gas cools through the X-ray emission and eventually form cold molecular gas in the cluster center. The typical X-ray cooling time scale is roughly 500 Myr. Jeremy et al., observed the Pereus cluster in CO emission lines by the SMA, and found several kinematical components that might be infall flows of molecular gas towards the central supermassive galaxy.
	HCN problem in AGNs. (from ALMA projects) HCN/CO line ratios are larger in AGNs than in star burst galaxies. The ratios change from about 2.0 for 1-0 line to about 0.5 for 3-2 line. The ratios for SB galaxies are alway as low as 0.5. This means HCN line could be related to AGN activity and may no longer be a good tracer of high density gas in AGNs.
	Extremely low frequency radio emission from the giant radio halo of galaxy clusters -- Galaxy clusters are usually enbedded in giant radio halo in which magnetic fields and relativistic particles (originated from the cluster center) mixes with gas. They found an extremely steep ratio spectrum (implying a high frequency cut-off) around the merging cluster Abell 521, which implies that the halo is difficult to detect at the well observed frequency 1.4 GHz. The spectrum of the halo supports the in situ acceleration of the relativistic particles through turbulent acceleration. (from Brunetti et al., 2008Nature_455__944B)
	Galaxies appear simpler than expected -- According to hierarchical theory of galaxy formation, the properties of an individual galaxy should be controlled by six independent parameters: mass, angular momentum, baryon fraction, age, size, and its recent haphazard merger history. But the recent first detection of a sample of galaxies through neutral hydrogen radio emission showes five independent correlations among the six parameters, thus renders these galaxies to be controlled only by a single independent parameter. However, their data doesn't tell us which this controlling parameter is. (from Disney et al., 2008Nature455_1082D)
	AGN: what can we learn from their variability (from a colloqium talk by Dr. Patricia Arevalo in YNAO on Mar. 3, 2009): X-ray variation is correlated with optical variation in AGNs but with a phase lag w.r.t. the latter. The phase-lag is larger at lower variation frequencies. The optical and X-ray variation may originate from different regions of the disk and the phase-lag seems to indicate propagation of fluctuations in the AGN disk.

• Towards a microquasar (jets from a stellar black hole), they observed broad emission line in the faint, hard states and narrow absorption lines in the bright, soft states, indicating jets become stronger and produce hard X-ray emission and broad line emission by illuminating the inner disk in the hard states, while they are suppressed by an equally massive hot disk wind that is produced by the powerful radiation from the black hole. The narrow absorption line is signature of the hot disk wind. This finding indicates that the stellar black hole can regulate its accretion process by itself. (from Neilsen & Lee, 2009arXiv0903.4173N or Nature paper )

	GRB photometric observation (from the talk by Dr. Jirong Mao at YNAO on Dec. 30, 2008) The gamma ray in GRBs is synchrotron emission from relativistic electrons in the relativistic shocks that was directly produced by somekind of physical burst, while associated X-ray, optical and radio bursts is believed to be synchrotron emission from electrons produced when the shocks sweep across interstellar matter (with lower energy). Another view to connect gamma ray burst with optical after glow is the anti-Compton scattering that promote low energy photons to produce the gamma ray. Currently the most popular model is the fireball model. But it still can not explain all observational facts. The current hot topics concentrate on GRB physics and the host galaxies. The evolution of the X-ray, optical and radio afterglows may be governed by the variation of microphysical parameters or the cooling of electrons (possibly the cooling frequency of bulk electrons sweep accross X-ray, optical and radio to produce the observed afterglows). GCN: Gamma ray burst Coordinate Network, a network of telescopes to observe GRB afterglow.
	The most powerful GRB: In the wee hours of the morning of 19 March, 2008, astronomers detected an extremely bright (naked eye) gamma ray burst from 7.5 billion light-years away (halfway across the universe) along the direction of the constallation Booties. It was brighter than a hundred-billion suns and squarely aimed at earth. The GRB is believed to be from the collapse of a massive star in a distant galaxy.
	Collapsar model of gamma ray burst with MHD (from the colloquium talk by Dr. Hohei Masada at ASIAA on Jun. 6, 2008) General porperties of GRB:  occurance rate = 1~2 events/day;  burst timescale = 0.1~100 sec;  released energy = 10^51~10^53 erg. the long GRB is composed of a series of short bursts with timescale of 1 sec. Classification: Long burst: 100 sec, formed from massive star collapse Short burst: 1 sec, formed from NS-NS merging or BH accretion (NS = neutron star; BH = blackhole) X-ray burst: sometimes occurs with a time scale of ~100 sec (several bursts after the gamma ray burst and before optical afterglow) In the massive star collapse model (for long burst), an accretion disk is assume to be already there when the central Fe core of the star begin to collapse into neutron star. The disk is an advection dominated accretion flow (ADAF) disk that is located deep inside the nuclear reaction shells. The inner most part of the disk has an extremely high density of 10^11~10^12 g/cm3 and extremely high temperature of 10^10~10^12 K, so that the material is opaque to neutrino. The trapped neutrino drag the matter to increase the viscosity to avoid turbulence in this region. Therefore, the inner disk is called a dead zone. (This is different from the dead zone around PPNs where dead zone is created by low ionization degree in the middle plane of the disk. ) In the outer disk where it is neutrino transparent, (assumed) magnetic field interacts with Keplarian rotation to produce magnito-rotational instability (MRI) and cause strong turbulence there. The turbulence also drastically increases the viscosity in the outer disk. The typical viscosity is 10^-4 in the inner dead zone but 10^-2 with the MRI in the outer disk. With this model, the short timescale (1sec) gamma ray bursts were produced by gravitational instability in the accretion disk. the long term X-ray bursts (100 sec) might be controlled by the fragmentation of the outer disk (due to cooling and instability) and the episodic accretion of the clumps from the fragmented outer disk. The MRI effect is necessary to increase terbulence viscosity and speed up the accretion of the clumps. It can reproduce the long timescale of 100 sec of the X-ray burst.
	TAOS detected a unusual gamma ray burst optical afterglow. (from the postdoc discussion led by Dr Li-Jin Huang on Nov. 29, 2007 at ASIAA)  Gamma ray bursts (GRBs) usually have a typical time scale of several seconds. Some bursts have a pre-trigger event (a smaller leading burst in gamma ray), while the others do not. GRB afterglow in optical usually appears within several minutes of the major burst. Then it decays fast, following a power law of time.  The physical model of GRB is still not very clear. We even don't know if all GRBs can be explained by a single model. One of the possible models is supernova (SN) event in other galaxies. The SN explosion produces the gamma ray burst, while the shocks produced in surrounding interstellar gas by the outburst materials (with a delay of several minutes) can explain the optical afterglow. Some other models may involve episodic jets produced by an unknown type of object (e.g. episodic accretion of black hole). TAOS detected the early stage of  the optical afterglow of a GRB just about 10 min after the major burst. The decay of the afterglow is much slower than normal power law of other known GRB afterglow sources. The detection was confirmed by all three telescopes running that day. This is the first time to detect so early stage of the afterglow and the slow decay is yet to be interpreted.