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--- courses:ast403:agn-types [2026/03/07 20:41] – [2. Radio Galaxiess] shuvo
+++ courses:ast403:agn-types [2026/03/07 21:33] (current) – shuvo
@@ Line 41: / Line 41: @@
 //Radio Lobes:// Enormous, twin clouds of radio-emitting plasma that straddle the host galaxy. These lobes can extend up to 1 Mpc (over 3 million light-years) across, making them some of the largest single structures in the Universe.
-[{{ :courses:ast403:cygnusa.jpg?600 | Fig3: A VLA radio image of Cygnus A, showing the two radio lobes separated by about
+[{{ :courses:ast403:cygnusa.jpg?600 | Fig 3: A VLA radio image of Cygnus A, showing the two radio lobes separated by about
-$\rm h^{-1}$ kpc and the jet extending from the galaxy to the right-hand lobe. Cyg A is a narrow-line radio
+/h kpc and the jet extending from the galaxy to the right-hand lobe. Cyg A is a narrow-line radio galaxy.}}]
-galaxy.}}]
 **Radiation Mechanism**
@@ Line 65: / Line 64: @@
 ===== - Seyfert Galaxies =====
-Seyfert galaxies are a prominent class of **active galactic nuclei (AGN)** first systematically identified by astronomer Carl Seyfert in 1943. They are characterized by **extraordinarily bright, point-like nuclei** and spectra dominated by **high-excitation emission lines** that originate from gas moving at high velocities.
+Seyfert galaxies are a prominent class of AGN first systematically identified by astronomer Carl Seyfert in 1943. They are characterized by extraordinarily bright, point-like nuclei and spectra dominated by high-excitation emission lines that originate from gas moving at high velocities.
-**1. Classification and Spectral Types**
+**Classification and Spectral Types**
 Seyfert galaxies are primarily categorized based on the width and presence of specific emission lines in their optical spectra:
-**Seyfert 1:** These exhibit **both very broad and narrow emission lines**. The broad lines originate from high-density gas in the **broad-line region (BLR)** moving at speeds of up to **10,000 km/s**, while the narrow lines come from lower-density gas in the **narrow-line region (NLR)**.
+**Seyfert 1:** These exhibit both very broad and narrow emission lines. The broad lines originate from high-density gas in the broad-line region (BLR) moving at speeds of up to $10,000 km/s$, while the narrow lines come from lower-density gas in the narrow-line region (NLR).
 **Seyfert 2:** These show **only narrower emission lines** (though these are still broader than those in normal galaxies, typically $\lesssim 1000$ km/s).
-**Intermediate Types:** Astronomers also use designations like **Seyfert 1.5, 1.8, and 1.9** to describe nuclei where the broad-line components are present but less prominent than in Type 1.
+**Intermediate Types:** Astronomers also use designations like Seyfert 1.5, 1.8, and 1.9 to describe nuclei where the broad-line components are present but less prominent than in Type 1.
-**2. Physical Structure and Central Engine**
+[{{ :courses:ast403:seyfert.png?600 | Fig 4: Spectra of a Seyfert 1 (Left) and a Seyfert 2 galaxy (right).}}]
+**Physical Structure and Central Engine**
+The energy for the nuclear activity is derived from a supermassive black hole (SMBH) at the center of the galaxy.
-The energy for the nuclear activity is derived from a **supermassive black hole (SMBH)** at the center of the galaxy.
 **Accretion Process:** Matter spirals into the SMBH through an **accretion disk**, releasing gravitational potential energy as radiation across the electromagnetic spectrum.
-**Spatial Regions:** The **BLR** is extremely compact (often $<1$ pc across), while the **NLR** is larger and can sometimes be spatially resolved, extending from **100 pc to several kiloparsecs** from the nucleus.
+**Spatial Regions:** The BLR is extremely compact (often $<1$ pc across), while the NLR is larger and can sometimes be spatially resolved, extending from 100 pc to several kiloparsecs from the nucleus.
-*   **Obscuring Torus:** A doughnut-shaped **torus of dust and gas** surrounds the central engine. This structure plays a critical role in the **Unified Model of AGNs**, which suggests that the difference between Seyfert 1 and 2 galaxies is simply a matter of **viewing angle**. If viewed edge-on, the torus hides the BLR, resulting in a Seyfert 2 appearance.
-**3. Observational Properties**
+**Obscuring Torus:** A doughnut-shaped torus of dust and gas surrounds the central engine. This structure plays a critical role in the Unified Model of AGNs, which suggests that the difference between Seyfert 1 and 2 galaxies is simply a matter of viewing angle. If viewed edge-on, the torus hides the BLR, resulting in a Seyfert 2 appearance.
+**Observational Properties**
+**Polarization:** Many Seyfert 2 galaxies, such as NGC 1068, reveal "hidden" broad lines when observed in polarized (reflected) light, confirming that they possess a BLR that is merely obscured from our direct line of sight.
-**Polarization:** Many Seyfert 2 galaxies, such as **NGC 1068**, reveal "hidden" broad lines when observed in **polarized (reflected) light**, confirming that they possess a BLR that is merely obscured from our direct line of sight.
 **Variability:** Seyferts often show **rapid fluctuations in luminosity** over months, days, or even hours, indicating that the energy-producing region is very small.
-**Multi-wavelength Emission:** They are powerful sources of **X-rays and infrared radiation**. Type 2 Seyferts typically show "harder" (higher energy) X-ray spectra because the obscuring torus absorbs the lower-energy "soft" X-rays.
+**Multi-wavelength Emission:** They are powerful sources of X-rays and infrared radiation. Type 2 Seyferts typically show "harder" (higher energy) X-ray spectra because the obscuring torus absorbs the lower-energy "soft" X-rays.
 **Radio Output:** While Seyferts are stronger radio emitters than normal spirals, they are generally much weaker than radio galaxies.
-**4. Host Galaxies and Environment**
+**Host Galaxies and Environment**
-Seyfert nuclei are found almost exclusively in **spiral and S0 galaxies**, particularly Sa and Sb types. Roughly **10% of all luminous spiral galaxies** may host a Seyfert nucleus. These galaxies are frequently found in **interacting or disturbed systems**, where tidal forces can drive interstellar gas toward the center to fuel the black hole. One striking example is **NGC 4258**, where a fast-rotating disk of gas around the central black hole powers water masers, allowing for a precise determination of the central mass.
+Seyfert nuclei are found almost exclusively in **spiral and S0 galaxies**, particularly Sa and Sb types. Roughly 10% of all luminous spiral galaxies may host a Seyfert nucleus. These galaxies are frequently found in interacting or disturbed systems, where tidal forces can drive interstellar gas toward the center to fuel the black hole. One striking example is NGC 4258, where a fast-rotating disk of gas around the central black hole powers water masers, allowing for a precise determination of the central mass.
 ===== - Blazers =====