Astrophysics - Galactic Profiles and Measurements
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What does the Sersic profile model primarily represent?

  • Spiral arms of galaxies
  • Intergalactic medium
  • Dark matter concentration
  • Elliptical galaxies and bulges (correct)

    • Type I profiles follow a double exponential law.

    False

    What is the central intensity in the exponential function represented as?

    I0

    The transition of the electron spin in hydrogen atoms is responsible for the ______ line.

    <p>21 cm Hydrogen</p> Signup and view all the answers

    Which of the following is a characteristic of Type II profiles?

    <p>Double exponential law with a break radius</p> Signup and view all the answers

    CO is the most abundant molecule in molecular clouds after H2.

    <p>True</p> Signup and view all the answers

    What is the parameter 'bn' in the Sersic profile used for?

    <p>Ensures that re contains half the light</p> Signup and view all the answers

    Match the following disk profile types with their descriptions:

    <p>Type I = Single exponential profile Type II = Double exponential with a break radius Type III = Up-bending in outer parts</p> Signup and view all the answers

    What is the estimated number of stars in the Milky Way?

    <p>100 billion</p> Signup and view all the answers

    The Dark Matter Halo of the Milky Way has a mass of approximately $10^{12} M_{igodot}$.

    <p>True</p> Signup and view all the answers

    What is the Hubble constant according to the 2018 Planck observations?

    <p>67.66 ± 0.42 km/s/Mpc</p> Signup and view all the answers

    The typical speed of stars in a circular orbit in the Milky Way is approximately __________ km/s.

    <p>200</p> Signup and view all the answers

    Match the following galaxies with their distances from Earth:

    <p>Sagittarius dwarf = 24 kpc Large Magellanic Cloud = 45-50 kpc Andromeda Galaxy = 780 kpc Virgo Cluster = 17 Mpc</p> Signup and view all the answers

    What percentage of the total mass of the Milky Way is made up of dark matter?

    <p>85.8%</p> Signup and view all the answers

    Photometry measures the intensity of radiation from astronomical objects across all wavelengths.

    <p>False</p> Signup and view all the answers

    What is the diameter range of galaxy clusters as mentioned in the context?

    <p>1 - 5 kpc</p> Signup and view all the answers

    What is the unit of luminosity measured in astronomical objects?

    <p>[erg/s]</p> Signup and view all the answers

    The flux F of an astronomical source is independent of its distance D.

    <p>False</p> Signup and view all the answers

    What is the formula for calculating bolometric luminosity (Lbol)?

    <p>Lbol = ∫ Lλ dλ</p> Signup and view all the answers

    The apparent magnitude m is calculated using the formula m = m0 − 2.5 log(F), where m0 corresponds to what value for F0?

    <p>3631 [Jy]</p> Signup and view all the answers

    Match the following galaxy classification methods with their descriptions:

    <p>Hubble sequence = Visual classification based on light concentration CAS classification = Model independent classification Photometric decomposition = Model dependent classification</p> Signup and view all the answers

    Which of the following is NOT a characteristic used in the Hubble classification?

    <p>Color of the galaxy</p> Signup and view all the answers

    Vega is assumed to have a magnitude of 0 for all wavelengths (mλ = 0).

    <p>True</p> Signup and view all the answers

    What is the significance of Jansky units in measuring intensity or surface brightness?

    <p>1 [Jy] = 10−23 [erg/s/cm2/Hz]</p> Signup and view all the answers

    What is one benefit of using Hα emissions in observations?

    <p>It provides good spatial resolution and is a very bright line.</p> Signup and view all the answers

    H I has better angular resolution than Hα.

    <p>False</p> Signup and view all the answers

    What causes the formation of H+ clouds in HII regions?

    <p>Photoionization of neutral H by UV photons emitted by young stars.</p> Signup and view all the answers

    The systemic velocity along the line of sight is represented as _____ = v(0) = vcosm + vpec,gal + vpec,M W + v⊙ + v⊕ + v⊕,rot.

    <p>vsys</p> Signup and view all the answers

    Match the following observational techniques with their characteristics:

    <p>Absorption stellar lines = Traces stellar movements and needs high S/N spectra Long-slit spectroscopy = Combines 2D image and spectrum of a region H I observations = Less sensitive observations due to dense cloud presence Datacubes = Reconstructed 2D image from spectral data</p> Signup and view all the answers

    What is one problem associated with Hα emissions?

    <p>Patchy emission and incomplete coverage in separate galactic parts.</p> Signup and view all the answers

    The Doppler effect is used to derive the velocities in galaxies.

    <p>True</p> Signup and view all the answers

    Cold dense clouds are primarily composed of _____ molecules.

    <p>H2</p> Signup and view all the answers

    What does the variable $v_{obs}(x, y)$ represent in the context of a star or gas cloud's velocity?

    <p>Observed radial velocity</p> Signup and view all the answers

    A flat rotation curve indicates that $v(r)$ is variable and changes with radius R.

    <p>False</p> Signup and view all the answers

    What is the unit of measurement for Star Formation Rate (SFR)?

    <p>[M⊙ / yr]</p> Signup and view all the answers

    The h3 parameter measures the _______ of the Line Of Sight Velocities Distribution.

    <p>skewness</p> Signup and view all the answers

    Match the types of galaxies with their characteristics:

    <p>Fast rotators = Flattened shape, disk-like rotation Slow rotators = Puffy, more spherical shape Rotational support = Rotation supported galaxies Random motion support = Non-rotating galaxies</p> Signup and view all the answers

    In a rotating disc, which moment parameter is expected to have an anticorrelation with velocity?

    <p>h3</p> Signup and view all the answers

    The third moment h3 and the fourth moment h4 provide insights into the shape of the velocity distribution.

    <p>True</p> Signup and view all the answers

    What type of galaxies are typically classified as fast rotators?

    <p>S0, flat E, spiral galaxies</p> Signup and view all the answers

    What describes a galaxy with a constant star formation history (SFH)?

    <p>ψ(t) = const.</p> Signup and view all the answers

    The fossil approach studies star formation history in galaxies at different redshift.

    <p>False</p> Signup and view all the answers

    What is the primary characteristic of a single stellar population (SSP)?

    <p>A single, infinitesimal burst of star formation.</p> Signup and view all the answers

    The _____ elements are produced in Type II supernovae in timescales less than 0.1 [Gyr].

    <p>α</p> Signup and view all the answers

    Match each type of age/metallicity with its description:

    <p>Mean luminosity-weighed age and metallicity (MLW) = Dominated by young and bright stars Mass mean-weighed age and metallicity (MMW) = Dominated by old and heavy stars α-enhancement = Relative abundance ratio of α-elements to Fe</p> Signup and view all the answers

    Which of the following is true regarding spectral energy distribution (SED)?

    <p>SED is the emission of a galaxy across the entire spectro-magnetic spectrum.</p> Signup and view all the answers

    Fe is produced in Type II supernovae with a typical timescale of 1 [Gyr].

    <p>False</p> Signup and view all the answers

    What can the relative abundance of different metals in a galaxy indicate?

    <p>The star formation rate (SFR) of the galaxy.</p> Signup and view all the answers

    Study Notes

    Galactic Observations

    • The Milky Way contains approximately 1011 stars and has a mass of roughly 5 x 1010 solar masses.
    • The central black hole has a mass of about 4 x 106 solar masses.
    • The disk of the Milky Way has a radius of approximately 10 kiloparsecs.
    • The mass of the gas and dust in the Milky Way is estimated at 10% of the total mass.
    • The dark matter halo has a radius of about 200 kiloparsecs and a mass of approximately 1012 solar masses.
    • The typical speed of stars orbiting the galactic center is around 200 kilometers per second.
    • The orbital period of the Sun around the galactic center is about 250 million years.
    • The total mass of the Milky Way is roughly 1.16 x 1012 solar masses.
    • Stars make up about 4.3% of the total mass
    • The central black hole accounts for approximately 0.0003% of the total mass.
    • Gas and dust make up approximately 9.9% of the total mass.
    • Dark matter makes up about 85.8% of the total mass.

    Nearby Galaxies

    • Sagittarius dwarf galaxy is located approximately 24 kiloparsecs away.
    • The Large Magellanic Cloud (LMC) is located between 45 and 50 kiloparsecs away and has a luminosity roughly 1010 times the Sun.
    • The Andromeda Galaxy (M31) is roughly 780 kiloparsecs away and has a luminosity of approximately 4 x 1010 the Sun's luminosity.

    Galaxy Clusters

    • Galaxy clusters contain more than 100 galaxies.
    • The diameter of galaxy clusters can range from 1 to 5 kiloparsecs.
    • Their masses are greater than 1015 solar masses.
    • The Virgo cluster is one of the closest galaxy clusters, located about 17 megaparsecs away.
    • The Coma cluster is a somewhat more distant cluster, roughly 90 megaparsecs away.

    Relative Velocity Between Galaxies

    • The relative velocity (v) between two galaxies at a distance (d) is related to the Hubble constant (Ho) and is determined by the formula: v = Ho x d

    Photometry

    • Photometry is used to measure the intensity of radiation from astronomical objects across a broad spectrum of wavelengths.
    • The atmosphere has regions (windows) that allow observation of some wavelengths of light.
    • The atmosphere blocks many wavelengths because of absorption.
    • The luminosity (L) of an object is the energy radiated per unit time, measured in [erg/s]. This is integrated over all wavelengths.
    • Luminosity density (Lx) describes the luminosity of an object in a specific range of wavelengths [erg/s/Å].
    • Bolometric luminosity is the total energy radiated across the full spectrum of light.
    • Flux (F) is the energy radiated per unit area per unit time, often reported in units of [erg/s/cm²].
    • The intensity or surface brightness is the measure of flux per unit solid angle.

    Photometric Decomposition

    • Photometric decomposition is a technique used to analyze the surface brightness distribution of galaxies.
    • This method involves measuring the intensity of light (I(r)) across the galaxy using isophotes (regions of constant brightness).
    • This information is then plotted on a magnitude scale (μ(r)).
    • Analyzing the PSF (point spread function) helps to model and analyze the blurring effect.
    • Functions like exponential functions and Sersic profiles are used to model galaxy profiles.

    Galaxy Kinematics

    • The 21cm Hydrogen line and CO emission lines are used to study galaxy kinematics.
    • The ionized gas (Hα) and absorption lines can also provide insights into galaxy kinematics.

    Galaxy Morphological Classification

    • Galaxies are classified based on their visual appearance.
    • Hubble's classification scheme is commonly used, focusing on the visual shape, concentration of light, and the presence of a bar.
    • CAS (Concentration, Asymmetry, Smoothness) classification is another system that is more analytic.

    Star Formation Rate (SFR)

    • SFR describes the current rate of star formation in a galaxy.
    • Measured in units of solar masses per year ([M☉/yr]).
    • Tracers include UV continuum, Hα, and other emission lines.

    Star Formation History (SFH)

    • SFH describes the star formation rate over the entire lifetime of a galaxy.
    • It can be constant over time, decline exponentially, or have various other patterns.

    Single Stellar Populations (SSPs)

    • SSPs represent a single, instantaneous burst of star formation.
    • They are used as a building block to model more complex stellar populations.

    Spectral Energy Distribution (SED)

    • SED is a plot of the galaxy's emission across different wavelengths of the electromagnetic spectrum.

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    Description

    This quiz tests your knowledge on various galactic profiles, including the Sersic profile and its parameters. It also covers important astrophysical measurements and characteristics of our Milky Way galaxy. Challenge yourself with questions about dark matter and the Hubble constant!

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